I see the need for recurrent training, myself. Things change. Wrapped tanks, evolving recommendations, star ratings (only for storage bottles so far), 3AL overstamps, and such, "happen," as do infrequent advances in inspection techniques and tools. Plus, being reminded of things and seeing previously unseen good and bad tanks (the instructor seems to have an endless supply of marginal, bad, and good tanks) helps when I do inspections for the local dive club.
One thing that stays with me is that most tanks fail when filled. As the owner of a personal fill station I have a strong interest in not having one fail, and relatively low interest in buying a containment unit unless one falls into my lap on the cheap.