If you are over weight or lean towards decapillarization (ie not athletic so you don't have as many blood vessels to get blood where it is needed) then it takes more pressure to get blood through the blood vessels to the tissue that needs oxygen etc....

So in general it is is an indicator of your condition and the health benefits you already have or don't have.

NOTE: i'm only talking about the good side of low heart rate, not the dark side others have mentioned.