I don't use subaccounts, i don't think it is really important for a lot of traders, particularly those who have a small portfolio. Subaccounts could be necessary for big time traders who have a lot of strategies and need to monitor them independently, other than that i don't see the need to set up a subaccount within an exchange. Neither do i like using multiple exchanges, because of the need to submit KYC in all of them.
That depends on the OPs trading situation. Sometimes, people are too organized, they want subaccounts as they have specific use case. So that will be their personal choice whether to create subs or not. But if you are just a small trader and not very active in trading, I don't think you need subaccounts. Just the main one is more than enough.
One edge case where subaccount is needed is when someone want to separate performance tracking and funds.
I prefer to do it this way because it's just cleaner, not messy. For example, you sometimes want to manage funds for meme coin specifically and the other for good fundamental cryptos.
These sub accounts helps a lot in that regard to give you insight about your performance on different startegies.