Ah, I remember when 4" phones were coming out - many here complained how oversized they were. Now I see tons of people using 4" screens all over campus, because it makes the web browsing, emailing, and facebooking all the more enjoyable when you have more desktop space to read more than 2 lines of text.
Another common complaint is why anyone would want to watch netflix on a tiny phone or on the go - these people must be kids who never had the joy of waiting in a Department of Motor Vehicles queue for two hours to renew their license. (When you have an eye test you can't do it online...) They give us larger screens, and then people say what would you use it for - how about watching netflix while waiting in a queue? Or maybe being able to see more than one field at a time when typing an email? Or perhaps seeing a text 4 or 5 back that you are responding to?
Personally, I miss my physical slide-out keyboard. When I am doing a crossword, I like to see the whole puzzle while typing a word. When emailing, it is nice to not loose 2/3 of the screen to a virtual keyboard. Like any computer, its about how much legible text you can get on the screen when typing long messages. I do a lot on the go, so pulling out a laptop and hotspotting it can be a bit too inconvenient, thus I prefer to do it on my phone.
In summary, a lot of people complain about how pointless the device is. However, the success of 4" devices along with tablets show there is a market for these larger screens. Now if only we could get the manufacturers to make inexpensive long battery life basic phones instead of just uber-powered smartphones....