I have a computer on each wrist. (Go figure, I like redundancy, but that's another thread. :biggrin
As opposed to looking at your wrist for Depth/time etc... then look at the spg for air, wouldn't it make more sense to have all that info in one place?
I will not dispute that having everything in one place is convenient, but the convenience of having your depth in front of you *far* outweighs it in the grand scheme of things, at least for certain types of diving.
If you're just diving on vacations in the clear, DM-guided waters of Cozumel, you can really go either way. On the other hand, if you're swimming a no-reference compass course at depth through murky water, keeping your depth in your field of view at all times (while working your compass and keeping your eyes peeled for the wreck, which should appear any minute now)... it's practically a necessity. Ascents, especially free ascents with minimal (or no) references and hovering stops can also place constant depth monitoring in the very high value bin.
As for your SPG, while you certainly should monitor it carefully -- running out of air being a keelhauling offense, at the minimum -- your SPG's readings do not change with anywhere near the same time constants as your depth (unless you've just blown an O-ring or an LP hose... or you breathe harder than the hooveriest diver I've ever seen). I may check my SPG a half dozen times during a "normal" dive (increasing that rate significantly if my perception of where the needle should be doesn't match reality), while I check my depth maybe even several times a minute on an unfamiliar site, wall dive, or other such occasion. (Of course, once it's time to ascend, I average about 3/4 of an eye on the computer at any given time.)
Anyway, long story short, for some types of diving, having nearly constant depth information is critical, so the computer on a wrist of the divers in those situations is certainly preferred. Air integration may be nice, but it's prohibitively expensive on wrist computers, so given the choice between wristing and integrating, wristing wins hands down (or up, or forward... whatever

). For divers who don't dive in situations where instantaneous depth information is as necessary, console computers have some positives and some negatives, so then it's just a matter of preference.