Tom – I use the small hole to run a light line around the front of the mast… I’m sure there is a technical name for it, but it just keeps the boom up against the mast.
the larger hole is for a “down haul” line for the boom that you would cleat off on one of the two cleats on the mast.
I am sure there are real sailors that can chime in with more knowledge than I have about sailing and rigging!