For all of the talk about how awesome (and big, don’t forget big) Big data is, one of the favorite tools in the conversion optimization toolkit, A/B Testing, is decidedly small data.
Optimization, winners and losers, Lean this that or the other thing, at the end of the day, A/B Testing is really just an application of sampling.
You take couple of alternative options (eg. ‘50% off’ v ‘Buy One Get One Free’ ) and try them out with a portion of your users. You see how well each one did and then make a decision about which one you think will give you the most return.