Should I clean up my inbox or not?

In the days of Gmail, I was always told that keeping one's inbox as clean and empty as possible. You know, move emails into folders etc, as long as they're out of the inbox.

I'm not sure if this is sound advice.

After moving to iCloud (and Apple Mail), I've found that my inbox is quite large. I have a handful of mailboxes, and even more smart mailboxes.

I understand that smart mailboxes don't move the messages out of the inbox.

Is it acceptable, performance-wise, to leave the inbox quite full, while using smart mailboxes as a quick way of organising?

Or would mailboxes be better?