Most of the stuffed heads on here had a powerbox fitted. I can see a mechanism where excess fuel squirted in indescriminately might cause hot and cooler spots on the head leading over time to microfractures that eventually join up or, if there's an issue with the cooling system prime it to fail. However, I can also imagine not all boxes are the same and some may be better (or worse) than others.
Given decent heads are becoming rare, I think it isn't worth the risk for me. Mine's pretty sprightly with the manual box. The auto is sluggish, IMO and I would probably chip it if I had one of them. Again, it'd have to be someone who knows what they're doing so as not to lunch that HP22 box.