Some additional points from the perspective of the benign violator (the other side of the happy interaction coin). I really enjoy being the benign violator with everyone, and am generalizing on my own experience:
Functionally, it's relationship-deepening for the reasons mentioned for the benign-violated perspective (trust, demo of personal knowledge, joy in making a friend happy by creating a positive, more memorable experience). I like deep, intimate relationships with people I choose to spend time with.
Signals symmetry - I'd enjoy being pushed in the pool too!
With new people: Nice way to build up rapport and establish mutual happiness-causing patterns from the get go (in my experience, most people like slightly risky social boundary violation and I like almost all my relationship types to be fun-loving). Goes wrong sometimes, but it's usually easy to adjust or even filter out people whose boundaries aren't conducive to my own joy.
Some additional points from the perspective of the benign violator (the other side of the happy interaction coin). I really enjoy being the benign violator with everyone, and am generalizing on my own experience: