Similar to the athletic competitionphenomenon (home field advantage), it is believed that your home toilet bowl has an advantage over all others, in that your ass is more familiar with the resting spot ultimately resulting in a far more comfortable and superior performing shit.
Guy 1: Dude, hurry up. We're gonna be late.
Guy 2: Hold on a minute. I gotta take a shit.
Guy 1: Can't you go at the bar?
Guy 2: No way man, I'm not giving uphome bowl advantage!
The closer you get to home after a long day, the more you have to shit. Your stomach is able to recognize how far you are from a toilet and proceeds to push the poop the closer you are.