It depends on the Animal,

My Dragon usually doesnt now, but when she was a baby she acted like she was aboreal. Now she doesnt like to go much hugher then a quick jump up or down.

Some love to climb though, others love to dig, and some are just plain lazy and want to sit around like Mine.

With dragons in almost all cases though, the bigger the better, The more room you can give an Adult, the happier they will be, Babies can get stressed in larger enclosures, so if they are under 10", i wouldnt put them in anything bigger then a 20L or so, and over that anything can really go because by that point they are eating good, and growing good ext. They do grow fast.

As for height of an enclosure, Id offer no lower then 24", because depending on the lighting you use, shorter can limit basking/climbing space. If you use a florecent UVB, like a repti-sun 10.0 (make sure its a tube, not compact/coil), then you want him 8" or so away from the bulb, so in a 20" enclosure he only has 12" of climbing, if the bulb is on top the enclosure, if inside its different. With a MVB, they need to be at least 12" away, with stronger ones further, so you need more space.

They like to climb up on a perch to bask. Dominant males will usually want the highest spot.
Ive also heard that some like to bask almost vertically to aid digestion, no sources on that as for articles, just theory.

And for the male, in the wild yes, personally im a fan of the 1 dragon per enclosure, so unless they see another outside i wouldnt expect that behavior.

Raul, do they do this out of habit if housed alone, or just when they have "Subjects"?

Ben