It's not like I prolong or extend the actual process. I sit down, let it reap, and when I'm done I continue to sit there.
Toilets have an amazing property I have not found elsewhere. See, in extreme cases where I ran out of toilet paper I actually had to get dressed after taking a shit, run upstairs and get some, and then run back down (because my neighbors don't get to see me running around with my pants around my ankles and shit in my ass). In those cases, the shit will dry in your ass and no matter how many tissues you use you are likely to get sore. If you stand up after taking a shit, presumably, it would also dry up after a while.
But whilst sitting on the toilet, the warmth from your ass heats the toilet water, creating a rather moist airspace in the pan between your legs. This keeps your left-over feces lubricated while you sit there and tend to other things. Like magazines. Now the purpose is manifold. After a blowout, your ass muscles have been stretched. You let them rest before you get up for convenience. Also, the worst thing is when you take a shit and wipe your ass, only to realize you weren't done. Sitting for a minute lowers the chance of that happening. Same goes for pee, which will replenish as you sit there. You can shit once and pee twice, all in one go-a-round.