You are most likely used to using a debit card for your business expenses, and there’s a problem with that. If that debit card is against your operating account and your operating account has significant funds in it and someone steals it, you lose it, whatever happens, for a certain amount of time they fraudulently get your money.
Your money may be protected because it is a debit account, but you may find out that there’s an extended amount of time before you actually can get access back to those funds. If you have someone take your card and they spend $3000, well, I've got news for you. It could take six weeks before you actually get access back to that money through your bank, even though it was fraudulent.
It’s another good reason to have a separate account that you’re really sweeping most of your money towards and only keeping enough money in the operating account for those operating expenses during that cycle of time.
If you are in a tight position financially, that $3000 could be a big deal to you. It can mean the difference between being able to pay the rent and not being able to pay the rent. Six weeks without that kind of money could be a long time. The easiest thing to do is not have so much access to that money, move it over into another account. You can always transfer it back and forth as needed.