One thing I really like about the 11″ MBA is the shallower front-to-back depth. With my older 13″ MBA, the front edge of the laptop is right under my wrists, which gets uncomfortable. With the 11″, the front edge is under the heel of my palm, which is much more comfortable.
The shorter height of the screen is also helpful as I use the laptop in front of my external monitor with the monitor elevated so that the top edge of the laptop screen bezel is just below the bottom edge of the monitor bezel. With this arrangement, the external monitor is just the right height. If I had to raise the monitor further because of a larger/taller screen on the laptop, that would be less comfortable.
These factors are particular to my (probably slightly weird) use case, but are reasons I would prefer a smaller MacBook Air apart from just having a lighter and more compact computer.