Why a long travel front DS?

Ok I am at the point where I am getting ready to buy new driveshafts, front and rear. I can understand a long travel rear with the leafs allowing for only verticle travel.
My question is this, why wold I need a long travel Front when theoretically the shaft never extends or compresses? Doesn't the control arms kinda keep it moving in a static arc, never actually causing lateral shift?

if its pre 97 with an hp front axle you should be fine with the stock d/s, i run an RK long arm at 5.5" and i cant max out the slip yoke on mine, i also use a front d/s on the back too, but i have 5" leafs with stock shackles so my flex is limited, if i had longer shackles i would need a different drive shaft but the one im using seems to work pretty good..Just noticed you have the 242, i have the 231, not sure if that makes a difference.

You basically have it backwards,the front travels way more than the rear(based on stock suspension).