Several things.......
Some is, no alcohol ever.
Some is, "I believe beyond the 8hrs bottle to throttle".....no, most sailplanes have no throttle. Alcohol is also a negative way to lose fluids, we can get dehydrated enough just from flying and then have to work harder to be physically ready for the next contest day. So what a person does at home is not what they may do at a contest. Even beyond 8hrs, senses are dulled a bit, so maybe part of the performance aspect.

Curious to see other replies.

As an aside, decades ago, for a contest finish, a call to the crew may be, "ice the beer" so the pilot knew they had home made and wanted a cold one. A contest for me (1996?) I called, "ice the baby bottle" (I had a several month old kidlet, wife was crew with said kidlet). I landed and was handed a baby bottle full of beer......sheesh, I love my wife....;-) this was at HHSC.....