Sure, tears off without a risk of anyone over pulling. Too much torque in said pull increases likeliness of excess TP being drawn out and hitting floor.

Aesthetics, print, whether you buy Charmin or some dollar general tp that's chocked full of splinters, print and design are presented neater over, rather than under: not presenting AS much.

Over doesn't have you knock your hand against the wall. Under could have the tp sticking to the wall (depending on how nasty the wall is next to one's toilet), under would make this difficult to grasp needed amount.

Parties and such, some fold the ends for presentation. No sense in folding if installed "under".

Thanks for asking for an explanation.