> what does the general public get out of polling?

The laypeople, not much. But for politically active people, not to mention political parties, polls are the best tool to determine where to do what. If you are way ahead in one race but neck and neck in another, it makes sense for parties and activists to focus their efforts and donations to the competitive race. There is never enough resources to focus on every race equally and to the fullest extent. Decisions need to be made. Polls are the best tool to make informed decisions.