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.