An em dash is used without spaces in most typography manuals. But that’s for typeset books, it’s not like everybody writes that way in casual communication.
I think surrounding it with spaces comes from people using a regular dash (the em dash is not readily accessible on the keyboard), then surrounding it with spaces to make sure it’s not interpreted as a dash.
I think surrounding it with spaces comes from people using a regular dash (the em dash is not readily accessible on the keyboard), then surrounding it with spaces to make sure it’s not interpreted as a dash.