Good question. I knew there was something else. Vehicles would have a ground plane as would a character. As they are kind of relative to how the model sits in the real world. But are optional.
The cliched and overdone cylindrical base is not part of the model. I know it sounds hypocrital because Ive mentioned putting a ground plane in, but the base...thats a maquette thing or something to be 3d printed to make it a final product look cool.

Generally though all turntable models would be framed well and rendered out 'floating' just as it is in production...so when in Rome....