Sure,

Recently, we had a FB campaign doing pretty good. We set up a $1000 per day limit and were getting about 5,000 impressions. Since we were getting a really good click through rate on those ads, we doubled spending the following day. Our expectation was that we would get around 10,000 impressions. What happened though, is we still only got 5,000 impressions. Our campaign (unchanged) went from serving at $.20 to $.40 that day.

FB does an excellent job of putting your ads in front of the right people, but it does better with fine tuning as opposed to big changes at one time.