> I live in the US and don't pay fees on transfers between my brokerage account and checking account. They take a few days to clear though
They're probably doing an ACH [1] transfer, which is net settled [2]. They take longer but are cheaper than wires. Fedwires, once transmitted from the sending institution, take seconds to be received [3]. They're real-time gross settled [4], i.e. faster but costlier [5]; many institutions waive (i.e. eat) these fees for clients with more than ~$50,000.
[5] Why? Because they're immediate and irrevocable. The first part means the bank has to use actual funds on hand, versus hoping a countervailing transfer cancels out the work or letting a profitable (relatively speaking) investment pay out. The second part means mistakes are more resource-consuming.