The only answer I can give to this is, "it depends."

Our service, BlockTrades, uses multiple accounts to separate our main @blocktrades which handles announcements and running our service from accounts such as this which have more limited access to funds for when we have to manually create a transfer to refund a customer.

Another user might, for instance, choose to have two accounts for hosting two distinct blogs.

So while I don't think there is an inherent benefit to having multiple accounts, there are definitely situations where a person would want to for organizational purposes.