At least according to Jobst Brandt, who is pretty much Jebus when it comes to this stuff, retightening is very bad for the cranks.

"Failure from "over-tightening" is caused by repeated re-tightening of properly installed cranks. In use, an aluminum crank squirms on its taper and, because the retaining bolt prevents it from moving off the taper, it elbows itself away from the bolt and up the taper ever so slightly. The resulting loss of preload, after hard riding, can be detected by how easily the bolt can be turned."

http://www.sheldonbrown.com/brandt/i...ng-cranks.html