I built my wife's LHT with Cane Creek SCR-5C (compact) levers, and mine with SCR-5 (regular). So I can give a side-by-side comparison, at least for that brand.
The only difference is the reach -- the distance of the levers from the handlebar curve. On the compact levers, it's 14mm shorter (meaning that the brake lever has slightly more curve to it). All other measurements are the same; the levers are 183mm long, the hood length is 84mm, on both.
The compact levers make a huge difference for smaller hands. My wife has average-size 'woman' hands, and the shorter reach fits her perfectly. Much less hand fatigue, and greater confidence when controlling the brakes.
-- Mark