It's not fully clear to me what you're trying to protect from, so i'll put the cases i consider from your message:
1. you want to protect your board in case there is some splashing, in that case you need to consider that dripping might short circuit the connectors that you didn't coat, whether it's a slow leak or a blowout. In the best case scenario, that your board was protected from splash, if you're not running any air over the board, it will run significantly hotter, many many components use the pcb as dissipator, therefore your reliability will decrease.
2. you want to protect from moisture seeping into the components, and degrading them. In this case, you should know that unless they come in vacuum sealed bags with dissecant, your components have already absorved most of the humidity they will absorv from the enviroment, this is a continous cycle, and doesn't really affect the operation of the board. If you wanted to conformal coat to protect from this, the board would need to be baked in a controlled fascion, a process that would take a few days. All the previous negatives mentioned about heat would still apply.
3. I think it was on this forum, that i read about members from very humid countries like Philipines, that do experience failure due to corrosion from ambient humidity, in that case, it might very well be more advantagous to coat, and trade the loss of reliability due to corrosion against the hotter running.