All or nearly all the occupants using the holes will be nesting solitary bees and wasps, which make partitioned cells that they provision with pollen (from whichever plants that particular bee species collects) or with paralysed prey (whichever prey are used by that particular solitary wasp), on which they lay an egg in each cell. The egg hatches, the larva feeds on the food supply, then pupates, and will over-winter until the adult season period the following year. In addition there will probably be some nests 'parasitised' by cuckoo bees and wasps (cleptoparasites) adding to the interest and diversity. Cleaning the hotel out would destroy all these efforts and the next generation of insects.
So life is simpler than for the whole garden or gardener - just leave well alone and watch what inhabits the holes every year (identification of the species of bee and wasp which are using the hotel would require good quality close up photographs for some species and an actual specimen for most.