this thread has soooooo much fail in it.
you guys need to start asking yourself why we want articulation in our suspensions.
here is a hint, its not for one reason or another, its for many reasons.
the most important reasons to have "flex" are to keep the rig stable and level regardless of the terrain and to keep the tires on the ground with weight of the vehicle against them to maintain traction. so you don't want to be dropping springs off the perches, then you are getting almost no ground pressure and you will loose traction, but at the same time you don't want to limit your articulation so much that the suspension cannot contour to the terrain.
there are a lot of factors that play in to how a suspension travels- link geometry, spring rate, shock length, spring height (coil), vehicle weight, spring length (leaf)
when talking about a link suspension:
in an ideal world you would figure out the maximum wheel travel based on your link geometry (which in an ideal world would be perfect geometry) then you would build and mount your shocks, springs, brakelines, driveshafts, vents, etc so that they don't hinder travel anymore
for example lets look at a hypothetical:
if you were to cycle your suspension with no springs or shocks, and you realized that you had say 6" of upward travel before your tire contacted the fender, or the upper arms contacted the frame, etc. you would then bumpstop to that. then you cycled it down and discovered you had say 8" of droop before your control arms were bottomed out against the mounts, or the joints had fully misaligned and your suspension was bound. now you know that you have ~14" of travel available to you, so you need a set of shocks that can travel 14" and a set of springs that can do the same. you would then mount your shock so that full compression of the shock the axle is all the way against the bumpstop and then mount a limit strap so that it is holding the weight of the axle at full droop.
in a leaf spring system you would adjust your shackle angle and length until you got the desired amount of up and down travel without inverting the spring or inverting the shackle, and then limit strap and bumpstop accordingly and mount your shocks the same way in the linked suspension (full bump and full compression at the same point, limited at full travel of the shock)
now, none of us live in an Ideal world with our XJ's. we have to work our suspensions around an existing platform, that means our link geometry will be less than Ideal. also, most of us aren't running coilovers or airshocks that have tune-able spring rates to give us the perfect amount of travel to keep suspension weight on the tires at all times.
since it is really difficult to get any extra uptravel out of our suspensions, due to all the stuff in the way, some people run longer bumpstops so that they can mount the shocks lower and get more droop out of the suspension by sacrificing up-travel.
my .02 is that you bumpstop enough to prevent your tires from contacting your fenders, your shocks from bottoming out, and your upper CA mounts from hitting the oil pan. and then you run a limit strap to prevent the shocks from being torn apart by the weight of the axle.