For statewide candidates, it's probably more a "look at me, I support..."

I do find them a little helpful during primaries or very local elections. Things like school committee, selectmen/city council, etc. Those elections are often very small and there isn't much to get people's names out. I can see who's running, and then do my own research. Or, just vote on the name you recognize because you saw the signs (which I'm sure a lot of people do).