How often do you move small recurring Bitcoin purchases off an exchange?

I buy a fixed amount of Bitcoin on a schedule, but I’m less certain about how often to move it to self-custody.

Withdrawing after every purchase feels unnecessary when the amounts are small and fees can vary. Waiting until the balance becomes meaningful is more practical, but it also means leaving more on the exchange than I’m comfortable with.

For people making regular purchases, do you use a fixed withdrawal schedule, wait until you reach a certain amount, or base it on current network fees? I’m interested in how people balance custody risk against the cost and inconvenience of frequent withdrawals.