It depends. Many of the Glorystar stations don't change that often and so won't require a rescan. Most of the ethnic channels don't move that much either. But in both cases, sometimes a transponder move occurs (it is usually first announced on the old channel, though) and that would require a rescan. If you want to keep up with the latest new channels and see which ones have been eliminated, then clearing out the channel list and rescanning should be done pretty regularly. You can take a look at my recent channel guide (in Excel format) posted in the main FTA discussion forum to keep up with what has changed (I put this information at the top of the cover page of the file). I try to update it pretty frequently, although lately it's only been once a month or so.