It makes sense, thanks. So you define your rebalancing trigger either in terms of percentage points difference or time of the year?
Yes, pick one. I define mine as January 1st (well, that's a holiday--so the 2nd, really) and June 30th. Semi-annually is probably too often to be honest, but I'm not going to go messing around with my original plan. (Nothing but regret can come from that!) Other people choose when one of their funds gets out of line by a fixed percentage--7-10% usually, I think?
There was a poster here in the MMM forums who wrote about 5 paragraphs on their rebalancing strategy--giving themselves lots of clauses, exceptions, addendums, percentages, dates, and footnotes. Pretty much giving themselves free reign to tinker whenever they wanted and be an active investor. I told them that it was no good and unless they could define their rebalancing strategy in one sentence, it wasn't worth the paper I was written on 'cause they could screw around too much. ...Happily, they changed it. :)