It's of keen interest to the tow pilot, but proper balance is also important to the person at the other end of the rope! Gliders can have their handling affected just as adversely as any other aircraft, it's just that with only two or three seats and maybe some water ballast the calculations are quite a bit easier. Often they just placard the seats with the required weight.
I used to fly ASK-15s. I was skinny back then and had to fly with 20 lbs of lead under my seat to meet the required minimum front seat weight. One of our other gliders, a Schweitzer 2-22, had its own lead weight blocks that could be bolted into the nose as needed.