When does weighted GPA get used?

So I’m looking around prepscholar for average GPAs and I come across certain top schools that have GPAs above a 4.0 . My school reports both unweighted and weighted GPA, however, everyone tells me that it’s my unweighted GPA that matters. I guess that I’m trying to ask is how come there are average GPAs above a 4.0 if the maximum unweighted is a 4.0? Do these schools use only weighted GPAs in their evaluation or do some highschools only report a weighted GPA?

Colleges weight GPA’s based on their own criteria. Unless the school specifically spells out how they weight HS courses, the best why to gauge your chances is using your unweighted GPA.
You need to check on each schools website to see if their weighting scale is defined.