That's effectively providing a definition of the latency he's discussing, not an explanation of why that's the sort of latency he finds interesting.
But I see he does goes on to say that he cares about game performance, rather than typing experience:
«
If, for example, you’re playing a game and start dodging when you see something happen, you have pay the cost of the key movement, which is different for different keyboards.
»
For me, I don't care about the time after switch activation, rather about time after the tactile feedback (the "click"). Ideally the character would appear on the screen at the same time as the click; not after, and not before. If a keyboard can 'cheat' and activate the switch before that and hide some latency, that's fine by me.
But I see he does goes on to say that he cares about game performance, rather than typing experience: « If, for example, you’re playing a game and start dodging when you see something happen, you have pay the cost of the key movement, which is different for different keyboards. »
For me, I don't care about the time after switch activation, rather about time after the tactile feedback (the "click"). Ideally the character would appear on the screen at the same time as the click; not after, and not before. If a keyboard can 'cheat' and activate the switch before that and hide some latency, that's fine by me.