Too often, soaring pilots release their tow at some arbitrarily predetermined altitude before reaching where they need to be, or after passing through lift and leaving it behind, or dumbest of all, in SINK… Know what average climb rate to expect from your tow plane for still air (no lift, no sink) and then observe what you’re actually getting throughout the tow. You need a sustained minimum of at least 300 feet per minute more than the average towing climb rate to be sure of gaining altitude after release.
Beginners are wise to tow higher than necessary in case they fail to make good use of the first available lift. On the other hand, those confident of their skills may choose to release as soon as staying aloft seems possible, just for the challenge. (A pilot who fails on the first try might also be one who could use some extra landing practice.)
Few things are more frustrating than falling out of zero sink from a position slightly below other ships while they climb away. Once you’re on tow most of the cost has already been incurred, so if you’re unsure (and especially if it’s still early in the tow) staying on a few seconds longer is usually a good idea.