Okay, you've got me almost speechless... I don't mean to come off as rude but I'm guessing you're being asked this by some one in IT who thinks all software is the same (big pet peeve o' mine):
RAM is cheap and it's a server! Reporting applications need physical memory, the more the better, as the data is held in physical memory so processing can happen more quickly -- it's all about processing speed. Also, why question the minimum requirements of an application (which are typically barely enough to get by)? Minimum reqs aren't questioned for an OS are they? -- okay, that's rhetorical, I use that at IT managers when they question why "so much RAM?" is necessary for any reporting apps. The app. isn't Excel, it's a specialized reporting/visualization app.
Oh yes, you'll definitely want the minimum--or more. As Toby said, RAM is incredibly cheap and we're talking about one machine that will impact any other machine connecting to it. Why NOT install as much RAM as possible?
Sorry, no article--trust the experience of the Tableau folks and the users on this forum. They won't lead you astray, at least not on purpose.