The crowding of criminal courts puts pressure on judges and prosecutors to resolve cases quickly. This provides defendants with an opportunity to negotiate a plea bargain, rather than engage in a long, costly trial. For most defendants, the principal benefit of plea bargaining is receiving a lighter sentence for a less-severe charge than might result from taking the case to trial and losing. But there are other benefits as well.
There is a risk that the prosecutor may end up recommending a harsher sentence than the one proposed as part of the plea bargain. Or, even if the recommendation remains the same, the judge may not follow it.