That's another good point. For those who have never sliced an item, it's not quick. For a guaranted slice, here's what we have to do:
1) Make sure we have a knife, clamp, and upgrade kit (if doing weapons and armor) for each item we are slicing. 99% of hte time this means getting them out of factory crates.
2) open the slicing window via the radial dial. Connect the clamp
3) Read the text in the window carefully to make sure you're reading the color/polarity correctly (if you read it wrong, you botch the slice, and **** your client off)
4) Slice the first wire after double checking the color
5) Slice the second wire
Through out all of this you are often trying to be polite to the client who is chit-chating with you.
Granted, all of these steps don't take forever, and all said and done, it probably takes about 20-30 seconds per slice. However, it's not an instant process. Also, even slicing a container, which only needs a knife and a clamp, will run the slicer some credits. So when you get those free slices (which I do as well), make sure you thank your slicer.
Now, I know that part sounded pretty whiny, so I'll mention why I still keep the skill. First of all, it's really handy to be able to slice your own weapons and armor. That saves you several thousand credits as opposed to buying pre-sliced gear. Second, if you want to take the time to either sit in a starport or else be lucky enough to have a contract set up with an armor/weaponsmith, it is a very lucritive skill. I've made upwards of 100K credits in 15 minutes before just slicing a few suits of armor. So it IS worth getting the skill. Just don't put the smuggler or slicer tag up unless you're looking to do some work.