I used a Generic lot as storage for my Collector Sim and placed a rocket, telescope and microscope there too. By putting all that stuff there, she avoided paying higher bills for having it all on her lot. In fact, she also had a 'faux' retail store where she actually lived. Her store/home ended up being quite luxurious, but her actual bills were only 32 simoleons a week. She successfully collected everything possible in the game at the time I was playing with her.
I've also used a Generic lot a couple times to build an art gallery and a photography studio for my Sims. The photography wasn't very valuable so wouldn't have contributed to the bills very much. But, my Sim didn't have the space to display them and I was doing a photography challenge at the time. Some of the paintings my other Sim wanted to keep around, perhaps to sell later, were expensive Masterpieces though that would've jacked up the bills for sure.
I haven't used Generic lots for anything else other than those two things. However, I can see how it would be cool to use them for a 'second' home or a vacation home for my Sims. :)
Happy Simming! <3