DF mentions many times on the Switch that 720p looks sharp on a small screen in portable mode. This is no different the bigger the screen the more noticable the pixels get.
I gamed on a 42inch 1080p screen and it looked super sharp. Going to 55inch 4k screen, i can tell if i am running 1080p instead of 4k.
Honestly anything around 30inches i am happen to drop resolution for preformance however on a big 4k TV i wont, due to how noticable it is.
It doesnt take a rocket science to see a difference, however it depends if its worth the preformance gap.
I agree with you there. I had a 21" monitor and for the life of me I was never able to tell the difference between 720p and 1080p in there. I was like, wtf are these people talking about?
It wasn't until I upgraded to a 24" that I started to notice the difference, and even then it was negligible.