My mentor said last year to use one, this year said do not use....kinda confused.
Welcome to the World of beekeeping!
I'm a newbie and don't know the right answer...I do know that out of all the Beeks I've talked to, the overwhelming majority DO NOT use them, therefore, that's the route I plan on going.
As a matter of fact, now that I'm thinking about if, I can't think of anyone who's told me they use them. Most folks I know refer to them as honey excluders.
I do know some folks that will use them selectively or as a queen includer from time to time.