Uh, plea bargains are for times when a certain jury decision is all but assured. They end up saving time and money so it can be better used to determine the guilt or innocence of those whom the facts aren't so clear cut.
Except that this isn't how they are used. This might be why they were first conceived of, but it definitely doesn't reflect our current system.
In reality, cases where the conviction is assured are those where they DON'T get a plea bargain offer, because the DA has no fear of losing and the wins are good for the prosecutor's record (which increases chances for promotion, and decreases chances they'll lose their position).
The people who are offered pleas are the ones where the DA is worried about a loss--the majority of cases in the US (easily) are the result of plea bargains. And the DA loves them, because it's so much less work on their end.
But, in reality, it comes at a massive price. Since the system is pushing prosecutors to make deals before ever going to court, they need to make their offer really attractive. They can't just make it increasingly lenient, so they trump up the charges they are threatening people with--literally adding every possible charge they can, as extreme as they can (even to the point where they would certainly never be able to actually prove the defendant deserved it in court).
And that creates another problem--innocent people get charged with crimes. And it happens more often than anyone is happy about. A system that revolves around plea bargains means that they are getting the absolute worst charges slapped onto them, beyond what they would deserve if they were guilty. That makes going to court increasingly terrifying, since their actual innocence means relatively little at the point where they are standing trial, since the prosecution has some kind of evidence against them.
Suppose your lawyer has told you that he thinks you have a 50/50 shot of winning. On the one hand, there's freedom. On the other hand, there's 10 years in prison. That plea bargain of 2 years is looking pretty damn attractive at this point...
And the worst part is when it comes to sexual indecency cases, where you find an absurd number of innocent people going to prison. It's so hard to fight these convictions, since our society is inclined to convict even in cases where the evidence is half circumstantial, half testimony. You get people going to prison (and being labeled sex offenders) even when they didn't do it, because accepting the plea is almost certainly getting them a reduced sentence.
But this is only part of the issue--the other part is that we are now creating punishments almost specifically to force people into pleas. The majority of armed robberies are actually punished as unarmed, for instance. The only substantial reason, then, that the armed robbery charge is so severe is to make the unarmed offer attractive. But how is it just that some people get unarmed charges, but others don't even get offered a deal and need to take the armed one, for the same crime in the same place