I leave the boom at the same height. That keeps the sail lower so more inclined to drive the boat forward than heel her over. BTW reefing became much easier after adding lazyjacks.  Barry

I'm glad you asked, I was wondering the same thing. But I was going to wait until after I had built my Dory before asking.   

Reefing is to reduce sail area. Raising boom when reefing doesn't maximize the effect of reducing sail as the center of effort on the higher sail area won't reduce heeling force as much. Better to lower yard when reefing to a boom.   

   Thanks for the responses.  I launched my Skerry for the first time yesterday and the winds hung around 10 knots with some small gusts a few knots higher.  The sail handled this easily, and I imagine that I would not need to reef very often since I don't think I would go out much with predicted winds beyond 15 knots.  That being said, it is good to know the process.  I can definitely see that the lazy jacks would be nice since it is a paid to have to hold both the boom and the yard in place while trying to tie the reefs.