Taxes recovery further while your body already has limited resources to work which may impact your ability to maintain performance on compound movements.
The benefit is a little extra stimulus to retain muscle with mechanical tension or metabolic stress. How much benefit it really adds is anyone’s guess. Not much tho
Biceps are a small muscle, that recovery quickly from high volumes. Should be alright to throw in a few curls. Delts with a few lateral raises or something should be alright too.
Careful with triceps tho because you need em to be fresh for all your heavy pressing movements. So bare minimum of pump work or nothing, save it for the heavy stuff.