If you connect your Twitter/Facebook/etc. accounts to your Google profile explicitly then Google doesn't have to rely on discovering it on its own by other mean

If you connect your Twitter/Facebook/etc. accounts to your Google profile explicitly then Google doesn't have to rely on discovering it on its own by other means, which probably increases the accuracy of tracking you around the internet by some small percentage. How does that benefit you? Then Google can serve you more targeted ads. Is that really to your benefit? No, but it is to the benefit of Google's customers--namely, advertisers.