That and the fact that unless you have two monitors often as you save the refresh happens out of view, when you’re not seeing the page, so you lose the immediate visual feedback of what actually changes. When you make minute touches to a design it’s annoying. When I hit F5 myself I can look at exactly what I’m interested and see if it shifted some pixels, if the font size is a bit better or worse...
Or have your editor and browser window tiled next to each other? Given how often FE development dabbles with design, using at least one decently sized monitor seems requisite.
And aren't FEers generally tweaking design in the DOM via a browser's developer tools when they're not sure what they want yet, copying back over into source once the design is finalized? Seems downright unpleasant to modify styling in the way you've described, and odd given there's a fantastic IDE in every major browser for styling exploration.
It's often much faster to make the change in the code directly than in the dev tools. For instance, I can very quickly apply a LESS mixin to an element, which would require knowing and making those specific changes to the raw CSS via the browser. The same goes for pretty much anything that's more than a one-value change.
Yes, I agree for what you’re describing, but that’s not the scenario I was referring to: the one where you don’t know how far over, how tall, how opaque, etc something should be and there’s no existing pattern to reach for off-the-shelf, like a mixin. Iterative exploration of design space.