From most that I have read cryo is something you use if you have a problem with residule stress in a barrel. Some have reported good results if they were experiencing group stringing as the barrel heated up. For example if you fire ten shots in fairly rapid sucession and the group starts out on target but the later rounds tend to move away (up and to the right seems a popular direction to move for some reason), you may have residule stress in the barrel that cryo may be able to help with. You may also have a pressure point on the barrel that cryo won't help.
Some custom barrel makers offer it but others say that they don't find any effect. That is probably because they are using a propper stress relief regime in the first place. Bulk barrel makers may not take as much care in the heat treatment.
As for barrel wear, most seem to agree that it does help reduce wear due to friction. Since the biggest wear is due to being exposed to erosive effects of the combustion gasses, it is somewhat questionable how much help cryo treatment would be. But it probably wont hurt.
Cryo treaters also claim that it effects different materials more or less, Carbon steel more, stainless steel less. If I was having a rifel made with a known barrel burner cartridge I would probably spring the extra few bucks for cryo on the theory that it won't hurt and may help. If it only helps your confidence and takes away some little doubt, it may be worth it.
