i read somewhere Set the settlement to a higher amount to pay a lower fee when transferring BTC. -snip-
Probably, the reason for that is to minimize the number of inputs when sending funds.
Because each of the pool withdrawal will be counted as one UTXO which will be used as an input for your transaction, the transaction's size will increase as the number of inputs increase.
If your usual transaction can only reach 0.001 BTC or slightly more, then weekly may be enough for you (
may have to use coin control depending on the wallet).
If you're not planning to spend it and will send it for later, then going for monthly is better so you'll only generate one input per month.