Holders vote on proposals: fee levels, token-emissions, treasury spending, contract upgrades. Voting power is usually proportional to tokens held or locked.
Value depends entirely on whether governance controls anything worth controlling. A token voting on a treasury and a revenue switch has a claim; a token voting on cosmetic parameters has a claim on nothing, however active the forum is.
Watch concentration. If insiders hold the majority, the vote is consultative at best. Also check whether a timelock and governance-quorum protect against a governance attack, where someone borrows enough tokens to pass a proposal that drains the treasury.
Related: dao, governance-proposal, governance-quorum, timelock