Here's an FAQ blue post about it:
Quote:
Below you will find the answers to common questions about the new Launcher being added this week. For more information and discussion, please review this announcement: https://forums.worldofwarcraft.com/thread.html?topicId=26262801168&sid=2000
Q. How much data is in each stage for a full Cataclysm installation?
A. In general, about 5% of the data is red (required), about 70% of the data is yellow (base gameplay), and about 25% of the data is green (extended data).
Q. How is data assigned to each stage?
A. Data is assigned to each stage based on the relative need for that data. Red is required to get into the game, yellow is data needed for base gameplay, and green is for variants of base game data (higher-resolution graphics, alternate sounds, other flavor data).
Q. How do I know when the entire game is downloaded?
A. The progress bar will reach 100%, and then will not be shown on subsequent launches (until there is a new patch released).
Q. Will I still be able to download patches from mirror sites?
A. Yes, standalone patches will still work.
Q. Will the downloader still use P2P / bittorrent?
A. Yes.
Q. Will large patches still be downloadable in advance through the background downloader?
A. Yes.
Q. Will it be possible to download the entire game before I begin playing it?
A. Yes.
Q. Is this mandatory?
A. No. Users will have the option of playing before all game data is downloaded and applied. They may choose to enter the game, or they may choose to wait.
Q. On patch days, will I be able to start the patch download before the realms are back up?
A. Yes.
Q. You are requiring a reinstall of the beta client. Does this mean I will have to reinstall my WoW retail client when I buy Cataclysm?
A. No. As with the prior two expansions, there will be a lengthy patching process to migrate users from the prior major version (3.0) to the new major version (4.0). Data for this patch will be downloaded in advance via the background downloader.
Q. Will I still be able to download a patch once and copy it to multiple machines?
A. Yes, as long as you have fully downloaded the entire patch. However, as with the prior expansions, patches from a previous major version (all patches prior to 4.0) will not work with the new major version.
Q. What if I have a low bandwidth connection?
A. After the initial beta release, users with connections below 1 MB/sec will be required to download all data before entering the game. Users with connections above 1 MB/sec will have the option of entering the game before all data has been downloaded and applied. Users at any bandwidth may exit the game and resume the download if they find the play experience undesirable.
Q. How will this affect new characters logging in for the first time?
A. If a player chooses to enter the game while content is still downloading, data for the introductory race video and zone fly-through will be applied at the loading screen to ensure a smooth game introduction. This is currently only functional for new worgen characters. Other races have not yet been optimized, which may lead to issues with the opening fly-through if they are loaded while content is still being downloaded.
Q. How much data is in each stage for a full Cataclysm installation?
A. In general, about 5% of the data is red (required), about 70% of the data is yellow (base gameplay), and about 25% of the data is green (extended data).
Q. How is data assigned to each stage?
A. Data is assigned to each stage based on the relative need for that data. Red is required to get into the game, yellow is data needed for base gameplay, and green is for variants of base game data (higher-resolution graphics, alternate sounds, other flavor data).
Q. How do I know when the entire game is downloaded?
A. The progress bar will reach 100%, and then will not be shown on subsequent launches (until there is a new patch released).
Q. Will I still be able to download patches from mirror sites?
A. Yes, standalone patches will still work.
Q. Will the downloader still use P2P / bittorrent?
A. Yes.
Q. Will large patches still be downloadable in advance through the background downloader?
A. Yes.
Q. Will it be possible to download the entire game before I begin playing it?
A. Yes.
Q. Is this mandatory?
A. No. Users will have the option of playing before all game data is downloaded and applied. They may choose to enter the game, or they may choose to wait.
Q. On patch days, will I be able to start the patch download before the realms are back up?
A. Yes.
Q. You are requiring a reinstall of the beta client. Does this mean I will have to reinstall my WoW retail client when I buy Cataclysm?
A. No. As with the prior two expansions, there will be a lengthy patching process to migrate users from the prior major version (3.0) to the new major version (4.0). Data for this patch will be downloaded in advance via the background downloader.
Q. Will I still be able to download a patch once and copy it to multiple machines?
A. Yes, as long as you have fully downloaded the entire patch. However, as with the prior expansions, patches from a previous major version (all patches prior to 4.0) will not work with the new major version.
Q. What if I have a low bandwidth connection?
A. After the initial beta release, users with connections below 1 MB/sec will be required to download all data before entering the game. Users with connections above 1 MB/sec will have the option of entering the game before all data has been downloaded and applied. Users at any bandwidth may exit the game and resume the download if they find the play experience undesirable.
Q. How will this affect new characters logging in for the first time?
A. If a player chooses to enter the game while content is still downloading, data for the introductory race video and zone fly-through will be applied at the loading screen to ensure a smooth game introduction. This is currently only functional for new worgen characters. Other races have not yet been optimized, which may lead to issues with the opening fly-through if they are loaded while content is still being downloaded.
Here's an image:
I would imagine it has more to do with your internet connection than your pc, but it could be a combination of both. Also, we all had to uninstall the game and redownload it to be able to use the new launcher, which is why it's taking so long. Most patches aren't even one GB in size, so I think it's a pretty cool new feature if they decide to implement it. I don't know for sure, but I figure they're just trying to make it easier and less frustrating for people to patch the game.