Research has shown that waiters get bigger tips if they repeat the exact words back to customers who are ordering food, and participants in one study were even more altruistic after they were mimicked. (They were more likely to pick up pens for the researcher who dropped them if they’d been imitated earlier.) Scientists theorize that, from an evolution perspective, mimicry promotes safety in groups by being a sort of “social glue.”
What this study doesn't mention is the pure narcissistic pleasure of being imitated. So if you want to wow an interviewer, for example, subtly adopt the body posture she has — leaning forward when she does, nodding when she does. Just don't go Marcel Marceau on her! Because then it would be weird.