Renting a storage unit is worth the cost if you're staying in college dorms, moving, serving in the armed forces, or remodeling your home. A storage unit is also beneficial for long-term storage of RVs and seasonal vehicles, especially when home parking is limited.
Conversely, storage unit rentals aren't cost-effective for keeping easily replaceable items that you won't need beyond a year. Be cautious about paying more for yearly storage than the items inside are actually worth.