[crazygringo]

I can design the same dark color scheme for iOS and Android, but I've still got to code it twice.

Or use the same dark colors for mobile-size and desktop-size in responsive, but still need to test it to make sure I got all the <div>s that appear in mobile-size but get hidden and/or replaced by other <div>s in desktop-size and vice-versa.

Or discover we thought we'd covered everything, but when you use the normally-touch interface with a trackpad on Chromebooks, the default hover state is still light-mode.

Etc.