When a baby is just wet and is wearing disposable diapers you don't always have to wipe the babies bottom or diaper area during the diaper change.
But if the baby is wearing cloth diapers then the baby should always be wiped down even if the diaper is just wet because the cloth diapers don't hold the wetness away from babies skin.
Disposable diapers use SAP or super absorbent polymer to absorb the pee and hold it away from the babies skin so the baby does not feel very wet or wet at all depending on how wet the diaper is.
If the baby has wet the diaper to the point of it leaking which has happened to my babies then the skin can be wet and you should wipe the babies skin down.
I always wiped my babies and toddlers diaper area down at every diaper change even when the diaper is just wet.
Urine turns to ammonia which can lead to rashes and also burn them.
You should always wipe the baby during every poop diaper change but if it's just wet then you don't have to wipe the baby every diaper change but you should.