When you want to be somewhere else, poolside/waterside. You can get these cheap and have a contractor put up all the drywalling,floor,electrical,ac etc.. for little. for about 3,800 bucks you can get one crane dropped and made turnkey. (10x10)
You must have a wife and kids you need to get away from. If I had distractions in the house I would consider doing something like that; nice little quite space to concentrate.