I get this question a lot on the tech line and I give a wishey washy answer with back up examples.
Most important thing to me is bare metal cleaning, no short cuts here period as it the most important step and I don't care how it is stripped, metal is porous and holds dirt/contaminants.
Now you blocked the primer and the call is do i clean, in a perfect world yes BUT 50% or so of the shops i talk to don't, they blow off wiping at same time with a prep-wipe.
Personally I clean when blocking a large area but sometimes don't on just a door a door or fender BUT no one else is in my playhouse to contaminate.