A glider pilot having a hand loosely on the release is good practice. A glider has options with an inadvertent release, while us tow pilots have very few with a low level kiting incident.

I can tell you I follow this practice when flying my glider. Also, when I am towing, once the throttle is wide open, my hand is loosely on the towplane release until I have a bunch of altitude beneath me!

Absolutely nothing wrong with this procedure, in fact, highly recommended.