Note: This is Virginiacentric. Remember that in Virginia there are truly discretionary sentencing guidelines (judge doesn't have to follow them and they cannot be grounds for an appeal). Also, if a jury trial is taken juries not only find guilt or innocence, they sentence. Juries do not get to see the sentencing guidelines and they cannot suspend part of a sentence. If the sentencing range is 20-Life a judge can (and usually does) suspend part of the 20 years; a jury cannot do this. Thus, the guidelines may call for a range of 7-9 years active sentence, but the jury has to impose the 20 years. A judge can suspend part of this, but most judges are hesitant to do so.
Immoral but Legal (IL) - Things which the majority view as wrong, but do not make illegal. Sometimes this includes matters in which we would point someone to a civil remedy - i.e. 18 year old girlfriend talked 85 year old grandpa into changing his will so that she gets everything instead of his children and grandchildren. However, quite often the actions are too small or the person involved doesn't have the resources to pursue a civil remedy. It also includes things which don't have a civil remedy - i.e. Bob calling Joe on the phone and telling him he is a "thug" (and hurting Joe's feelings). Sometimes an act may be IL because of the circumstances surrounding it; in Virginia a threat against a non-family member can result in a conviction for assault, however a threat against a family member cannot because the domestic statute requires both assault and battery.
Tolerated Illegal (TI) - These are things which the majority of citizens tolerate as being illegal, but only so long as the punishment is not onerous. A lot of the crimes herein are "for your own good" statutes. They are tolerated, but not truly accepted by a large enough portion of populous. On the lower end they are things like fines for not having the proper tags on a car or general speeding. On the upper end are things like underage possession of alcohol or possession of marijuana - both of which (at least in Virginia) have the option for a first time offender to allow the defendant to complete some sort of probation and not get convicted.
Minor Punishment (MP1) - A little time in jail or some secondary effect on the rights of the convicted. The people you see coming and going from misdemeanor criminal court every day are facing these punishments. A weekend in jail, 8 days of trash pickup, 10 days with work release - all the way up to a few months in jail or a driver's license restricted or suspended. This is where the majority of misdemeanors are going to end up and where a lot of first time, non-violent felonies are going to be (probation, no incarceration).
Moderate Punishment (MP2) - 6 months to 3 years. Usually, this is a plateau reached by people who have received a number of minor punishments, whether they proceeded from misdemeanors or felonies or (most likely) a combination of both. However, some non-violent felonies start out toward the bottom of this range, such as possession with intent to distribute cocaine (which Virginia's guidelines start at 7 months). As well, some violent acts which are felonies fall within this range, such as battery of a police officer (for which the statute mandates 6 months in jail, but the guidelines begin at 7 months).
Heavy Punishment (HP) - 3 years to 8 years. This is where more serious or multiple conviction non-violent felonies end up. It is also where a lot of first time violent felonies (malicious wounding) are located.
Serious Punishment (SP1) - 8 years to 20 years. Combination of violent felonies (robbery, abduction, & use of firearm in a felony). Often, this level is reached because the defendant's prior record is significant. Non-violent felonies can reach this high if aggravated (massive prior record or multiple convictions for drug sales).
Severe Punishment (SP2) - 20 years to Life. Almost always serious violent felonies. In Virginia punishment at this level is often because the defendant demanded his jury trial and got sentenced by a jury to more than the sentencing guidelines call for or a judge would have given. A few non-violent felonies make it this far. In Virginia an example of this would be distribution of cocaine 3d offense, which carries up to life in prison.
Death - Self explanatory. Currently reserved for aggravated murders. May be extended to rape in the near future.
The amount of time for MP2, HP, SP1, and SP2 are approximations based upon the reactions I've observed from defendants to potential and actual sentences. While there would obviously be variations from case to case, these are the levels where I noticed different reactions. MP2 does not draw extreme reactions in most cases; most defendants seem to see this just as part of their lives or perhaps as a cost for doing business. HP is where pushback begins. The Defendant figures that 3 years will probably mess up his life and 5 years definitely will. He will weigh his options much more carefully and is more likely to take a trial if he thinks there is a chance of winning. SP1 is where irrational pushback begins, particularly in the younger defendants. Older, more court/prison savvy defendants are more likely to make rational choices here. It's always the 18 to 24 year olds that think 10 or 15 years is an impossibly long period of time to do in prison and demand the jury trial despite being warned that the evidence is overwhelming and that the jury will probably punish him in the SP2 range. SP2 is where it is often rational to go to trial no matter what. If a 30 or 40 year old has guidelines which call for 30 years in prison he is facing a life sentence whether the sentence is technically "Life" or not. Often - perhaps the majority of the time - an SP2 sentence is the result of a defendant who would have gotten HP or SP1 if he had taken a plea offer or even made a bald plea of guilty, but chose to take a jury.