I read that sometimes they promote a no-hoper to see what kind of money or votes he can draw. Also, it seasons the expendable Newbies in the rough and tumble political arena.
That can make sense in a state with a lot of small districts where politicians can move from one district to another. Some political novices shop districts moving from one to another. You have to have money to begin with to pull that off, though.
Precisely how silly gilly Gillibrand got her start. Moved upstate NY ran as a gun loving conservative Dem, leaked a 911 call from her opponents drunken ex hooker wife, and wala, she's in Congress waiting for her Senate seat to open.