apart from being very nice to drink on a hot summers day, what is battement frappe a preparation for?

Frappes are preparatory for petite allegro. For example, jete dessus...

Thanks Gina.
I always think of Frappe as also being a wonderful opportunity to work on that turnout and trying to keep the upper thigh in its rightful place. also a good exercise (as most barre exercises are) to think of one's centre, alignment, placement, posture and poise. Deportment too
A wonderful exercise for strengthening the instrinsinc muscles of the foot including metatarsals and instep etc. It is a step that helps develop elevation (one can make good use of the floor here to help with the strong movement that the exercise requires). Please feel free to offer any input.