I do not punish players like that when real life gets in the way of our little fantasy game. The closest to that any groups did that I have ever been in was award half XP for missed sessions, basically awarding them as if they were NPCs for the night.
What's appropriate just depends on the game.
I've used single-party-tally XP in some games, where the PCs are a group doing stuff together
and expectation is every player makes every game if they can. 4e and 3e/PF suit this approach, especially in Adventure Path type play. My 4e Loudwater game ran level 1 to 29 over 5.5 years on a single XP tally, and no one missed out from missing a session.
Individual XP works best with my current open megadungeon 5e campaign, multiple groups, highly variable groups, no expectation that players make any particular session - in fact it's nearly impossible. There it would make no sense to call it a punishment for a PC played on Sunday to not get XP because he wasn't in the Tuesday game or the Saturday game, and XP is an individual reward for successful play.