I must confess, I've never been a fan of traditional experience points. Across my entire GMing career, I have almost always ignored them, and simply doled out level-ups when I felt they were appropriate (usually once every three adventures or so). Most of my players over the years haven't complained about this, so it just became gaming status quo for me.
When I set out to design Great & Small, however, I had to wrestle with the concept again. XP advancement is arguably one of the core assumptions of D&D, one that has followed it through every iteration and edition. But I just couldn't bring myself to like it enough to include in G&S.
The reasons why are probably less interesting than what I replaced it with: automatic advancement in your character's niche lore after an arbitrary number of adventures determined by the BM, with an advancement-by-skill-check system (an idea adapted from the original version of Bunnies & Burrows) for lores outside your niche.
I did this because I prefer to reward player commitment, investment, and participation over mere bookkeeping, but also because a game about animals ultimately isn't likely going to have "bash down doors/kill all the monsters/take all their stuff" as its main focus.
But, it occurs to me that leaving level-ups solely to BM fiat could itself degrade into a "level up just for showing up" system. So, here's an alternative scheme I'm considering for the expanded version of the game, should it ever come to fruition.
Advancement is based on XPs awarded for the player's level of participation, decided by consensus vote of the other players if there is a dispute (the BM and disputing player would both abstain from this vote). The system uses a unified XP table for all characters, as follows:
Level 1....XP 0
+20 points per level for each level over 12.
XP Awards Per Session:
0 = No-show or no participation
1 = Minimal participation or partial session
2 = Average participation
3 = Epic participation
Advancement in your niche is automatic once you earn the required number of XP. Transferring the XP to a non-niche lore still requires prior planning and the skill-check system described in the Quick Start rules.