My Current Thoughts on XP

As with many things, I've gone through a few different approaches to awarding XP and/or levels over the years. Until recently, I had taken the view that the thing to do was to not award XP at all, and instead give out a level every three sessions (or, in 5e, one session for 1st level, two for 2nd, and three thereafter).

However, I've gradually settled on a solution that I think works, which I intend to stick with long-term.

#1: XP Should be Awarded, and Should be Awarded Immediately

I've concluded that it is indeed better to award XP. As discussed previously, I divorce the XP budget for encounter building from the reward, and this allows me to give awards for other goals, but the principle is sound.

The other thing I've concluded is that it works best if XP is awarded immediately - as soon as an encounter is won, a quest is completed, or whatever, the PCs get the XP. That way, the PCs get immediate reward, which is a good thing.

#2: Levels are Awarded At the End of a Session
This one is fairly straightforward - once the PCs gain enough XP to gain a level, they gain that level at the end of the session, with the consequences applying immediately at the start of the next session.

Ideally, I think I'd prefer to handle this by awarding levels at the end of the adventure, and certainly requiring the PCs to be taking a long rest. However, given the prevalence of multi-level adventures, enforcing the between-adventure principle would be difficult. Likewise, I don't want to enforce a long rest because it's entirely possible that the session-break won't match up neatly with that - especially in the current paradigm of very short sessions.

#3: Everyone Has the Same XP (and Levels)

Again, this one is straightforward - everyone has the same XP total and level, regardless of actions in the game, attendance, or any other factor. I just don't see any benefit of doing things otherwise.

#4: Sessions Per Level

Assuming a session of 3-4 hours played once a week or once each two weeks, I'm inclined to think that the approximate rate of advancement that gives the best results is indeed one level per three sessions (except in 5e, where 1st level is probably one session and 2nd level is two).

#5: About Level Drain

Level drain has, of course, largely dropped out of the game, which is probably a good thing. However, for editions that do retain it, my inclination is that this should not reduce the character's XP total. Instead, a lost level should indeed be just that. However, as the characters go forward, each time they gain a new level they should instead gain two such levels until such time as they have again caught up.

However, that does need some further thought, as I'm not entirely convinced that this is the best approach. I do like the "catching up" approach, and I do also like the "you don't lose XP" approach, but the rate of recovery may need tweaked.