After only one year keeping bees I've come to believe that you should do something about those cracks, gaps and alternative entrances. The bees don't guard them much if at all - hive beetles waltz right in through them, and the beetles will hide in any spot that the bees can't get to. Before hive beetles it probably wasn't worth worrying about, but if they are a problem in your area maintaining a small single opening might help keep them out.