To the Crown, the benefit is that it obviates a trial and the expenditure of time and resources that entails, especially as those are under severe constraint as it is. The Crown is also not certain of a conviction even at the best of times, and in a case such as this, where mens rea is at issue, the outcome is more in doubt than in other cases, such as the original Bosma trial. From the Crown's point of view, a guilty plea on lesser charges is definitely preferable to a possible acquittal, and when the accused is not a danger to the public it is a much more viable option.
The judge is charged with making a decision in the public interest. If Crown and defense both agree on a plea resolution, it is unlikely the judge will refuse it without compelling reasons.
Normally, plea deals serve the public interest, because they prevent further clogging of the courts, do result in the accused paying some penalty (incarceration or other), and uphold the administration of justice. When done badly, as in the KH case, they cause a public outcry. But most are reasonable solutions.
Greenspan must consider the case against his client fairly strong, or he would not be taking this course. If he thought she were "innocent" he would not be making a deal, but defending her stoutly as he did the accused in, for example, the Mistie Murry case and the Mohan case. When the accused is just guilty, he represents the client making a guilty plea, as he did in the Muzzo case, where he didn't get Muzzo "off" but by pleading guilty and showing remorse, Muzzo was set up for better parole prospects later on, though he still received one of the longest sentences ever handed down for his type of offense.
