Elton has the short description of the notch nailed. There were some detailed set up descriptions posted a month or two after the LTD came out that are a lot clearer than the manual. I'm away from home and fighting a very slow and intermittent internet connection so searches for the instructions posted previously have not gone well; otherwise I'd post a link.
In my opinion, the better notch is the one between the ears. The majority of tabs I find fall in two ranges; 32 to 33 and 45 to 46. The LTD only lets me set one notch, and it is not quite as precise as just notching 32 and 33 or 45 and 46. I have also found nice pins and jewelry that were in the 32 to 33 or 45 to 46 ranges. As a result of my experiences I'll generally set a low discrimination level and listen to all targets and, based on target density and how I'm feeling on the day I'm hunting, I'll make the call on choosing to dig the 32 and 33 or 45 and 46 numbers or not.
Cheers,
tvr