Ability to store all your gear inside wthout it touching the sides of the 2 man tent thus getting everything wet ,
Ability to get dressed standing up, instead of floppign around like a fish trying to get dressed / undressed
Ability to sit in the porch area while it's raining, brew up and watch everyone else sitting in the tiny 2 man tent fully zipped up ..
There are pro's and cons to everything
I would always go as small as I can put up with.
My biggest tents are a Vango Equinox and Jack Wolfskin Time Tunnel.
Both of these I can sit in a chair with inches to spare. I can be bolt upright on my knees with inches to spare, and to enter the tent is no more than a bow.
I feel no need to be able to stand up in any tent.
The only tents I can't sit bolt upright in, are the Akto (95cm) & a Lightwave that I believe is 105cm high.
The best tent in the world, the Hilleberg Nammatj 3 (GT) has the perfect combination of headroom, width, strength and weight for this 6' 3" middle, middle aged, slightly stiff, Homo Sapien.