720 ITT is a recommended climb temp in the PC12 PIM, Normal Procedures section 4.11 "Climb", Also Flight Safety teaches this habit. They say the recommendation comes from the manufacturer but I can't find any evidence of that.

Like said before. Has to do with taking care of the engine. We had a catastrophic engine failure in a TBM and had to dead stick it 60 miles for a safe landing. You DON'T want that to happen to you. You have one engine, take care of it.