Depends on the trainer. Smart ones have calibration apps so you won’t be over or under reporting power, dumb ones you just don’t want the tyre slipping.
Dumb one, but happy to have bought on a whim several years ago, keeping me sane having never been used until covid kicked off. Was getting some.slippage after changing tyres so will work out how to have it pushing more firmly.
Depends on the trainer. Smart ones have calibration apps so you won’t be over or under reporting power, dumb ones you just don’t want the tyre slipping.