Roller rockers

Just watched an episode of Horsepower TV . . . can anyone explain why roller rocker arms help to increase horsepower? Is it just a wear issue? I thought I knew, but their explanation was more HP, I thought it was mainly a wear issue. Rocketman

Less friction, and they allow faster valve opening and closing rates when combined with roller lifters if it’s a push-rod engine…

They eliminate side thrust on the valve stems which allows more aggressive cam profiles and larger lifts without getting ridiculously short valve guide life in exchange.
Putting roller rocker arms and using a stock cam gains you nothing but maybe longer valve guide life.

Roller lifters can follow a more aggressive cam profile than regular lifters can.