Automated bots tweeting and retweeting are sometimes helpful, but other times not, especially if they are pure spam.

According to Pew Internet, it estimates that over two-thirds of tweeted links to popular websites are posted by automated accounts. That's a huge number!
It also estimates that 500 of the most active "suspected bots" are responsible for 22% of the tweeted links.

Pew Research: Over 60pct of Tweeted Links Are Posted By Automated Account [pewinternet.org]