The purpose of renters insurance is to protect your interests around the home, including your personal property and any liability incidents which may arise. Renters insurance will cover your personal property both in the home and when you are away from home, even when you are away on vacation or some other expedition away from home.
When you rent a storage unit, you will usually be offered a sort of insurance policy to protect your property while it is in storage. The reason this secondary policy is offered is twofold: the storage facility is not liable for claims against loss or damages, and your home insurance policy is not designed to protect your property while it is being stored. This type of coverage is not usually the best protection and may limit the coverage to theft or even have other clauses which limit the liability of the company.
Insuring the property in your home is less risky than insuring the same property in a storage unit. Not only is the stuff in your home expected to be safely locked up when you are away, storage units have little or no control over the character of those who use the facility. For all the storage unit knows, the next person who comes in the door is there to case the location for a late-night theft. In your home, the odds of a malicious visitor still exist, but the danger is much lower because your home is private and not available for anyone who happens by.
Instead of purchasing coverage through the storage facility, which may not provide with the best protection, you can pick up a separate personal property policy that covers the things you have in storage. This method of protecting your property works best for most people because it extends the coverage on your property to wherever you have it at, whether it is at home, in a storage unit, or wherever it being safely kept.