For me, it’s a way to show participation without affecting the outcome. I read all of the proposals. Some of the reasons I vote Abstain are because I don’t feel strongly either way, think it’s not a bad idea, but just not the right time for it, or disagree with some details, but not the basic concept. As a WG0 Steward, I started voting Abstain to stay neutral.
Voting participation is also something that affects a person’s Karma score, the tool the DAO approved through AIP-132: Karma - Reputation system for ApeCoin governance contributors.