Conversely, previously I had deleted all Keywords, for most of my campaigns, that had never recorded an impression. My sites performance slumped for several weeks for all the subject campaigns, but not for those untouched.
My recommendation - yes monitor regularly and make changes when you need to - but not too soon and not too often.
Make sure you base any assessments of trends on data from at least 1 week, preferably a month.
[edited by: Pengi at 2:37 pm (utc) on Oct. 9, 2006]