I don’t think I’d ever turn specific notification off 
Mostly due to security.
Monzo providing instant notifications for every single thing offers piece of mind - if, in the unlikely event, somebody has obtained my card details somehow and decides to register my card on Amazon, I would have no clue that an active card check had been done and I would only realise something was amiss when that mysterious person sticks a couple of 4K TV’s in their basket 
It’s always nice to have options but I don’t think Monzo should offer the choice to disable one of their USPs 
If I ever want my phone to be quiet, I just stick DoNotDisturb mode on 