1. Yes, it is harmless; another girl cannot impregnate her or overpower her, so any threat of rape or bad genetics is thrown out of the window
2. It's 100% positive social proof; men hitting on her boosts her value, no matter what, but she can't entertain ALL of their pursuits, or her value will take a hit ("she's a slut!"). But other women complimenting her and entertaining their advances? Super hot. Guys get turned on even MORE when OTHER women are all over the girl he wants. He imagines orgies.
3. Women know women. They knew how to touch a girl and how to react intuitively.
When you start getting really good though, you can touch women's asses, boobs, waists, faces, etc quite easily and will little to no resistance. Even when I grab a girl's ass and slightly overstep my bounds, she just grabs my hand, moves it and then goes back to flirting with me or she'll mock offense, slap me on the chest, and then start flirting with me harder!
One girl I work with, a dancer, I took a handful of her ass while her friends were playing with it and she got super surprised, had a "gafaww" face and said "Hector! Haha, that's the one time you get a free pass!"
5 minutes later she sticks her ass out and tells me to grab it again.
Hector