Honestly both sides suck at using them and they have little impact on the national elections as is. But both sides want them to continue existing. They make it possible for challenger politicians in small races to get their names known.
There's no research proving or denying this claim, but as anecdotal evidence: Mike Bloomberg spent more on advertising than any candidate in history for his primary election campaign (~$500 million), which he lost spectacularly.
People often credit Facebook Ads for Trump's 2016 victory, and it's an interesting claim considering that he spent substantially less than Bloomberg on the platform (~$40 million).
