Can you elaborate on that? I'm not sure what you mean, having a separate brokerage for cash management.
I have two brokerage accounts at Fidelity. One is named "cash" and the other "investments."
There are no investments in the cash account, only cash. This is the account that I use for direct deposit/debit, where I have a debit card, etc. It's the only account that has permissions to transfer funds in/out of Fidelity. I don't use Bill Pay, but it is supported. I don't write checks, but it looks like it's an option, from Fidelity's website:
Checkwriting is available on nonretirement brokerage and cash management accounts with individual, joint tenant, business, and trust registrations; custodial accounts, health savings accounts, mutual fund accounts; and traditional and rollover IRAs. You must be at least 59½ years old to add checkwriting to an IRA. Checkwriting is not available on Roth IRAs.
The investment account is where I hold investments. I don't have a debit card for this account and no cash management features are used with this account. I'm not even sure if it's possible since it's locked from transferring in/out of Fidelity?
The only benefit that I see to having a separate cash management account is it puts your cash into a different silo. So if someone gets your debit card (which I don’t use) or your checking account number, they can drain all your investment cash. If it’s in a cash management account, only that cash is susceptible. Technically you’ll get it back, but when and how long.
I also have margin on my brokerage (which I don’t use either) but in a pinch I can pull out a boatload of cash. Can’t do that with a cash management account.
As I noted above, I create the same silo using two brokerage accounts. As far as I can tell, the only differences are the FDIC insurance and the sweep account. The cash management account is FDIC insured and doesn't sweep to an MM fund, so you don't get as good of a yield on the cash balance.
I don't have a large balance in the cash account, so I don't care about FDIC and if someone gets access, it's no different than any other checking account. I'm guessing that checking accounts have better regulation around them if they are compromised, so maybe that is another difference between the cash management and brokerage accounts? But this isn't something I lose sleep over.
I've read that there's some way to always have a zero balance in the cash management account and automatically transfer funds from the brokerage's MM fund when needed, but not having done it, idk know the details on how it works.