Oh, I'm not saying that it's a problem with YNAB per se, but if you have joint finances and one partner isn't willing or able to get on board with it properly, then it does become a chore, in that it requires that extra bit of prodding.
We can definitely allocate the mortgage in advance, but we're in the US where it's been paid by cheque, and DH never sends the cheque out on the same day each month, so I'm never exactly sure what day it'll come out. We're going to set up automatic payments, though, so hopefully that will get better. But other things, like some utility bills, change each month, so if that's being paid by him, I either have to be watching the bank account to see when the money comes out, or (again) ask him every few days to put it in himself.
The money is meant to go into the savings account as he only gets paid for the academic year, so we're meant to allocate a certain amount of each month's salary towards living on in the summer. I'd like it to go into the savings account so that we earn a wee bit more interest in it in the meantime.
I know it sounds trivial, and I know it's not the fault of the software if both partners are doing it properly, but in my experience, it's led to a bit of extra stress between us, and put me in the position of the shrewish missus trying to find out where the money's gone, just to keep the thing up to date.