Every year out there produces exactly one day people still bring up a decade later, and it is almost never Friday. Saturday is where the consensus lands — the set that gets permanently attached to that year's name, the one your friends will describe to you in detail whether or not you asked.
Which makes it the day where standing position becomes a competitive sport. People start staking the main field hours ahead of the headliner, and the actual skill is holding something close while still catching sets on the other stages all afternoon. Get that math wrong and you spend the day walking.
The Sahara after dark is the other reason. Largest tent on the grounds, packed well past whatever its stated capacity is, bass and heat and body density combining into something you can still feel the next morning regardless of who was playing.
Send it to whoever you would want to lose your voice next to in the desert.