The mash profiles actually refer to the body of the beer. Light bodied beers are typically mashed at lower temperatures for a longer time which results in a more complete conversion of the sugars and lighter body. Heavier beers are mashed at a higher temp which results in less complete conversion, and some complex sugars are left that are unfermentable. These unfermentable sugars result in residual body and sweetness suitable for full body beers.
If you are brewing a light lager or wheat beer or something with less body, try the lighter mash profile. For something like a Porter, Stout or other full body ale, use a full body profile. For average beers, use the medium setting.