why is it optimal to adjust ride height through the pre load of the spring?

why is it optimal to adjust ride height through the pre-load of the spring as opposed to adjusting from the lower mount of the shock?

i understand its best practice but am unsure as to why, Talking with my colleagues many find it difficult to accept/understand this as being optimal or having any benefit over the typical method of using the lower shock. I've also experienced that some BC coilovers actually insist on not adjusting the preload of their spring from their default settings. I suspect its to do with the operating range of the shocks but struggle to explain that with my lack of understanding. this would help a tone if I could understand this a little better as I hate teaching people a method without an explanation.

cheers matt -

I assume this is the type with two adjusters, one for the spring seat and one for the damper body in the lower mounting point of the suspension?

There are two schools of thought on this, with the only real difference being the travel on droop - if the adjustment is made at the spring platform, it is adding pre-load to the spring and limiting its ability to fully extend on droop, whereas if the spring seat is just pre-loading the spring by, say, 5mm, it has very nearly its full travel available to it when the adjustment is made with the body mounting thread.

There are times when the first may be most useful, to limit travel, and I know many prefer to use it, but my preference would be the latter to get full travel when the suspension is unloaded.