I don't generally use an excluder, but have a few JUST in case.. I have the old ZINC flat stamped excluders from my mentor that MAY have been used once or twice in all the years he owned them, along with a few newer ones, the welded wire type, most of which have never been on a hive..
Finding you NEED an excluder and don't have one is a real pain..
Might be because you want to use it as an "includer" or because you really do need to keep that queen with a desire to wander out of the supers.. Always good to have!