For me doing kegels when I start going soft actually deflates my penis more quickly. The PC muscles serve to squeeze. If blood’s leaving the penis, it pumps it out faster. If blood in entering the penis, it serves to add that extra *oomph* to your engorgement.
On the flipside, if you have strong PC muscles you can shoot your load stronger. Likewise if her PC muscles are pretty strong, and she knows the mechanics of a guy’s ejaculation process, she can literally suck the semen out you while your cumming. Of course if your both cumming simultaneously, nature takes over and both sets of PC muscles pulsate in-sync. No need to kegel here, as it’s involuntary, but having strong muscles intensifies the experience.