Fully on-chain: slow, expensive, and completely binding
Fully on-chain voting means every vote cast is itself a transaction: the voter signs and submits it, it costs gas, and it's recorded permanently in the governor contract's state. The advantage is that this is as binding and transparent as governance gets. There's no separate step where someone has to take an off-chain result and manually implement it, the vote tally lives in the same contract that will trigger execution, so the outcome is enforced by the same code that recorded the votes. Anyone can independently verify the tally by reading chain state directly, with no reliance on a website staying honest or a database staying uncorrupted.
The cost of that guarantee is real friction. Every vote is a transaction, which means every vote costs gas, which means voting can get expensive enough to discourage participation from smaller holders, worsening the apathy problem from a purely economic angle rather than just an attention one. It's also slow in the sense that proposals typically need a fixed on-chain voting window (days, not minutes) to give token holders a fair chance to see and respond to a proposal before the window closes, and that fixed window can't easily be compressed without undermining the fairness it's meant to provide.