I've ridden a tandem bicycle with my wonderful wife - we rented one to ride around Sausalito for a day. As fun as it was, there is no way I'd ever buy one for home use.
For one thing, they take up a lot of space. Probably about as much space as 2 bikes take up. For another thing, if my wife is sick or out of town or for some reason can't go, I'd look pretty ridiculous riding a tandem bike by myself. Do they even work with one rider?
Wouldn't wanna be downwind
The tandem bike
“I'd hate to be the downind person on a tandem bicycle.”