As I mentioned in another post, as your org grows, there's going to be an infinite amount of things people push, and pushing back is hard. If you have to stop and write a consensus document for every single one, you'll be doing nothing else.
If you have the authority to tell people no in the first place to make it stick, you have the ability to write that in a wiki page. You can go full FAQ mode for the miscellaneous stuff as it comes up.
Documenting the why is really important, so you don't get zombie decisions self perpetuating in your org and allow for change.
spoiler alert: it isn't hard and this is what we do at my startup that is currently experiencing hyper growth and is on multiple "unicorn" lists