Long tow ropes lessen the effect of tow plane prop blast on the glider.
Less chance of the glider dropping a wing on takeoff. This is a very
noticeable effect with my Libelle.

Tow ropes less than 200 feet long are just too short. 275-300' seems
about right to me.

Got towed with a 60' rope once (really short field). No problems but it
required much more precise flying.