I just did some quick searching because I wanted to know too so take this w/ a grain of salt.
Higher pressure cap
Pros: raises the boiling point of water more than stock. This will decrease the risk for hotspots in the cooling system such as the heads.
Cons: More pressure and therefore more wear on the cooling system components.
and the low pressure cap would be the reverse.
I would think that with a healthy operating coolant system as well as a proper mix of coolant/water you wouldn't have to worry about the boiling point or hotspots..