Twitter is a company with management that doesn’t understand what it has. They think they’re a media company that sells ads. They’re really a data company.
They should compete with Bloomberg, Google News, peer-reviewed science journals, CNN, and Pinterest.
Salesforce might want them (turns out they don't) to bolster their social credibility, which is a thing that Benioff (CEO) has been obsessed with this decade. They might get useful data around individual relationships, and help build a social graph to figure out valuable customers.
A Twitter acquisition can make sense if they do it right. Salesforce has proven (with Heroku) they can acquire non-core business and allow them to run independently enough while still giving Salesforce benefits.
It wouldn’t be my first pick, but it’s not as bad as Microsoft.