The extra water volume is a positive thing in terms of waste management. More volume to dilute the waste into. Decreased oxygenation with taller tanks could be an issue, but this problem vanishes, or at least is minimized if you have a sump.
Completely agree foresure. Its just that a lot of people, including myself, only look at the volume of the tank when starting out new. It seems like we all talk about tanks in gal more often than dims, and I thinks dims are just as important, if not more. Like you said, you can increase water volume and waste management by inlcuding a sump of fugue.
For example, a looking at 2 tanks on the market
40gal-36x15x16
50gal-36x15x18
Thats a 10gal difference, so one a newbie like myself would like to think that you could keep an extra 2" of fish (1" per 5gal), but you are not really affording much more actual room for a fish. It will be easier to keep you water params in check in the 50gal, but I am not convinced that you could keep more or larger fish in the 50gal vs the 40gal.