The racetrack has you brake regularly, in the same spots, and near the same speeds for the same durations at each of the spots you hit...
The street doesn't. Often, the street needs you to brake when the pads/rotor is relatively cold. Some riders need/prefer to brake lots, and so the pads must work well when hot, too.
Progressive action on a streetbike would scare the scat (this word was edited by the bb software!) out of most riders. This is when the brakes grab harder the longer they're applied without moving the lever.
Most riders on the street - and many on the track - prefer linear action - more brake is dialed by squeezing more on the lever.
So, for the street you probably want a linear pad that works just as well both hot and cold, with good stopping power. This pretty much describes an HH pad.
Race pads can need more heat to start to work - the dual-carbon types, for example. Some pads work better with different rotor types (e.g. cast iron vs stainless).
The general consensus is to ride street (and occaisional trackdays) with HH pads.
Track-dedicated bikes can put more race-oreiented pads on (duh...).
My trackbike is shod with Vesrah RJLs.
