So I'm still working, but I feel like this question is a reasonable one even when you're still employed. I figure in 5 years or so I'll want to replace my car and that'll be a $7k chunk of change at least. I could create a YNAB category and fund it at $110/mo for the next 5 years, but I don't really want to have an extra 7k sitting around in my checking account for years before I need it -- I'd rather send that money to Vanguard and pull it out when I actually need it. Plus, my engine could die tomorrow and not be worth the price of fixing, or alternatively everything could keep running just fine and we could hold on to this vehicle for 10 years. Impossible to predict, thus difficult to accurately budget for.
The conclusion I've come to is that YNAB doesn't really work for large, infrequent and unpredictable expenses. My current solution is to use YNAB for all day-to-day spending and recurring monthly/annual bills, and for the bigger stuff that I run into once in an unpredictable while (a car, moving expenses, hospital copays) pay as they come in. My rough mental annual budget is about ~10k more than what YNAB shows, which is enough to cover a couple of those big expenses in a year if necessary. In 2016 we did in fact move countries, buy a used car, and have a baby, so we did come close to that 10k mental estimate, but most years our unbudgeted spend is much lower. :)