Offering tenant insurance for your self storage facility increase your profits for your facility. It increases revenue by giving a chance at proverbial "checkout" to giving clients another avenue to spend more money.
This money spent, however, is money well spent in the eyes of a consumer. This is not a gimmick, people have differing levels of value and a tenant will know if they are or are not storing things of importance to them when using your storage unit. The likelihood is, that if a tenant feels they are storing things that they need to protect then they will opt-in for tenant insurance.
Offering your tenants peace of mind when they store their stuff on your property. This value and peace of mind is the foundation of a quality relationship between renter and rentee.