I like to glue up miter joints so that the excess glue will not be a problem for later varnish. Mostly for picture frames.
I cut my stock first to long lengths and then I varnish all sides, several coats.
After well dried, I dado or cut out the waste where the picture and glass will be inserted.
Now I miter cut my sections to size and glue it all up. Any excess glue or glue that would otherwise spill over to the finished face side will end up on a varnished piece of wood. This glue will not soak in, will easily wipe off and leave a clean finish. If sanding is required, no problem. Sand and then varnish when done.