With digital platforms like steam where there are zero chances of a game not being in stock prepurchasing benefits are limited to the few bonuses they give out like exclusive skins and crap.

I have bought a game at full price over $40 maybe once a year but not a prepurchase unless they had a free beta before the game was released. Nearly all of them were multiplayer games where I had played the beta with friends and we ended up putting in hundreds of hours.

Sadly, not enough games have free versions to try out so most games I purchase for $40 or less.