A PSI(R), Pre-Sentence Investigation Report, is a document that will be used to assist the court in determining your sentencing. The report usually contains a factual narrative of the offense committed, your personal and criminal history (if applicable).
Specific questions should be directed to your attorney as he or she knows the particulars of your case. Good luck.
Pleading to a PSI, as it is known in Texas, is simply pleading guilty to the Court and allowing the Judge to assess punishment after requesting and considering a Pre-Sentence Investigation report compiled by a probation officer. These reports include details of the offense, victim impact, criminal and personal history of the defendant etc...After considering the PSI report and any other evidence submitted at the punishment hearing, the Court can sentence the defendant to anything within the allowed range of punishment. This may be anything from deferred adjudication probation to the maximum, twenty years in your case. Unless you have unusual or compelling reasons to consider "pleading to a PSI," I would think the risk may be too high, especially if the prosecutor is asking for prison time.
Straight, unconditional “pleading to a PSI” is most often not an effective defense strategy. It’s a historical byproduct of a defendant “throwing himself at the mercy of the court,” and mercy is not a judicial commodity often dispensed by most Texas Courts. Basically it sets a defendant up for a sentence that could be harsh and outside what is reasonable for the particular defendant and the facts of the case. Thus, absent an extremely sympathetic defendant and a case with specific factors that demand leniency, pleading without a plea bargain to the court, subject to a PSI, seems to approach mal-practice. If a defendant is looking for moderation and compassion, looking to a jury is most often the best course.
Bottom line, discuss this with your lawyer and ask questions. Why do they advise you to plead to a PSI? Can they give you good reasons? If not, I would keep asking questions and make sure that this strategy is in your best interest and not just a way to wrap up the case.
I have written an article precisely on point here if you are interested.