For someone who habitually hand-holds and tries to shoot at fast shutter speeds to eliminate camera-shake fast lenses give the advantage of keeping the ISO low. They also make for nicely softened backgrounds which give an added perception of sharpness to subjects. Mind you that 17-55 is pretty sharp wide open. In my book at any rate.
Using both the 17-55 and the 70-300 (a sluggish f4.5-5.6) pointed up the difference today as dusk approached and I was shooting under tree cover. Looks like I'm going shopping...
17-55 - 1/160s, f2.8, ISO560
70-300 - 1/100s, f5.3, ISO1600