For the most part we have rent (mortgage), food, utilities, insurance, and day care (have you looked into the cost of this?) all locked up and well-budgeted, but sometimes someone leaves the door open or the hose on too long and we have an unexpectedly high utility bill. One time my wife left an entire bag of groceries behind the car and accidentally backed over it. When COVID hit and my dad was simultaneously suffering from a suppressed immune system we had to stop leaving the kids with my parents and up our daycare expenditures quite a bit. These sorts of problems aren't really problems for us, we can just cover the added expense out of our "emergency savings" bucket, but if two emergencies happen back-to-back sometimes that bucket gets depleted and we have to draw from "vacation savings" instead. Fortunately we're able to fill these buckets with hundreds of excess dollars a month, so they are usually adequate. I could see it being problematic if the buckets filled at a much slower rate.