I discussed this with a Dom friend of mine as I couldn't understand why he would want to share his property. The reason that he gave was because that way, everyone would know what he had and how good it was. Ownership would be his and only his and they would envious. Letting someone use something of yours gives you some control but is more than just telling someone how good something is, they can actually experience it but then must give it back.

Because I struggle with jealousy it's taken me a long time to understand the attraction but I think I can now.

I guess it could be a very possessive act really.

Just my two cents worth, great question.