I would think it depends on the type of diving. I reckon if ive got a backup computer in which you can complete the dive safely id do that. Your not compromising anyone or anything by doing that and I would be doing the next dive on only one computer as I would have before I ever got a second one. Not to mention there’s my buddy with his computer(s). And if we got separated then obviously your aborting anyway. So then there’s two of you with 2/3 computers between you still. If that isn't a more than required safety margin I don't know what is. This is how I separate computers from every other bit of dive gear, because by their nature they are separate. If anything other fails yeh your aborting, obviously anything relating to your air source, tank, first stage, DV's, not least because its all interconnected. Drysuit flood; getting cold. Fin strap breaks, cant move easily etc. These are all direct hazards to overall physical and dive safety. I believe that you can be too cautious however, others don't, its personal opinion.
Now I've got two masks, if say the mask skirt of my primary one has been damaged putting it on and I have my second one in my pocket, i'll change it mid-dive, I aint aborting just to throw it to one side and waiting get back in the water later. In such a case having a spare mask is not only just convenient. But obviously more importantly because otherwise aborting is a must, due to safety and the possibility of becoming fully flooded without being able to clear. I view computers in this way. But then im only a recreational diver who’s only been to 30m! As I said I would imagine it depends on the type of diving.
Now don't get me wrong it also depends on the scenario. If my computer is knackered because ive had it crushed (along with my wrist) from a bit of wreck then im not gonna be wanting to hang around admiring the red misted scenery. Same goes for getting my face accidentally smashed by my kick boxing buddy. But if its a relatively calm situation ill want to keep going
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