Consistency in the design of a user interface is often a good thing. Re-using a small set of salient, simple interactions within a single application, or across a suite of applications, allows users to apply what they've learned during one interaction to many others. It makes the user interface predictable, thereby making it easier to use. Scott Berkun made a similar point in an extended meditation on consistency way back in 1999, a point that still stands.
I'm a proponent of consistency. I've written about the usefulness of standards and guidelines, one way of supporting consistency among applications. However, it's misapplied when the benefit of a local optimization outweighs the benefit of enforcing consistency throughout an application. It's also misapplied when a presentation style developed for one domain (like radio advertising or visual web) is applied to a wholly different domain (like VUI dialogs). I was recently handed a dialog by a company's branding expert that read like this: "Press 1 to do x
At times when I'm arguing against the misuse of consistency I say (with a nod to Emerson) that I'm practicing exorcism of possession by hobgoblins.