Because the legislature sets a range of sentences, then setting a specific sentence (or probation) is clearly a discretionary act by the court.
Judges are required to demonstrate that they have weighed the evidence.
Review of sentencing helps develop consistency and develop standards (also it might reduce appeals, because just reviewing sentences is cheaper and quicker and generally addresses one of the appellant's prime concerns).
Upon review, the court can:
Those are the factors that the court should weigh when discretionizing about sentences.
This is motivated because there has been so little review action on sentencing, courts are just following the form of reasoning but not doing it substantively, and with TIS, we no longer have parole as a mitigating factor.
As a rule, judges are frustrated that they don't have more information at sentencing time (even pre-sentence reports don't always get done), and a lot of the time it's the DA who will recommend a sentence.
This decision has had little substantive impact: people are still getting the heck sentenced out of them, without much consistency or reasoning. McCleary was the outlying case, really: it was amazing that the sentence got modified. We see sentences overturned, but often that's for a specific legal reason (e.g., wrong sentence imposed, wrong credit given for pre-trial incarceration, or something).