I have a 27" monitor, and I use a 3px border for the active window border, so I suppose I'm wasting some space.

I have two 27" 4k monitors and don't want to waste a single pixel. I did not looked how the gap feature can be enabled/disabled and I really hope the default is disable contrary to the new "drag window" feature that can not be disabled and that regularly disrupt my workflow.

(I know that an upgrade add the ability to disable the drag window feature, it's just not available in FreeBSD yet).

i3 user here with 42" monitor: I still wouldn't waste the space for gaps/elegance/eyecandy.

But, as with anything, this is a matter of personal taste.