Ok ynab. When creating a target which one would you choose? Refill up to or set aside each month?

Usually it's set aside, I'm still not totally clear what refill is for

its for when you know you only need a certain amount max for the month, so if you didn't use it all the previous month, then you just need to add enough to make sure you have you max again for the current month. And example would be you go to a personal trainer twice a week for 150 dollars each session. So your target is 1200 dollars a month. If you had to cancel once last month, then you only spent 1050, and you have 150 left. You are still only going to spend max 1200 this month, so you don't need another 1200, you need to refill to 1200, by allocating another 1050.

Another example is your insurance deductible money.