The active state has 2 uses:
* It gives some visual feedback that a button has been pressed.
Otherwise, tapping a button gave no feedback that the tap had
occurred. Particularly on a phone screen where fat-fingering is
easier, hitting the 'save' button in particular gave no hint that the
file had actually been saved. Which causes some anxiety.
* It suppresses all mouse taps during the activation time. For example,
this helps keep tapping say an overflow button from selecting text in
the editor.