crappie rods are long for several reasons.
1. trollers use long rods so that they can get the lure out away from the boat...which spooks the crappile less. also trollers use different length rods on the boat so that they can keep there lures from getting tangled.
2. for jigging, long rods allow you to drop the bait right over the structure holding the crappie so that you don't have to place your boat so close to the structure...which would require you to cast to the structure possible making more noise and again, spooking the crappie.
those is just a couple of examples.
for trolling, i use the roger gant "the difference" rods in 9 ft length. and for jigging i use the sam heaton rods in 9ft. the longer rods certainly have their purpose but i find them cumbersome in a boat as small as mine. but i'll buy a few when i get a bigger boat.