I can't claim I know what they intended, but I like to think they wanted it to work something like this: You want a boost? Sure, you got it friend! Just go out and bite someone. Like, right now.
You know, reward with inherent risk.

Either interpretation is wonkey though.

I have to admit, though, I just plain like the idea of a Vamp on a team of runners, they need more power in a pinch, so he turns to them and asks "So who's going to man up and let me suck on their neck? Common man, it's for the mojo, you know I don't swing that way!"

Incidentally, how do 'knocked unconscious' and 'requires strong, critter-focused emotion' work together? I always wondered.

That. Is. Awsome. Added to my list of quotes.

Lucid dreaming?

Not necessarily. The 'drained in the last hour' part could be like a catalyst. Kind of like how you can burn fat in your body for energy, but you generally need to burn some calories first or you won't even be able to get started. So, you have that reserve, but it is only tapable if you've eaten recently.

For vampires, the stored essence might usually be bound too closely to them, but when they've just fed, the feeding frees it up a bit to incorporate the new essence.

That said, I agree, you may as well house rule it to be usable whenever, because as a self defense mechanism, it doesn't make sense that you can only activate it when you've just, essentially, won a battle.

I'm not saying you can't justify it: you can always justify anything magic.

"It's Magic." the second shortest all-encompassing argument.

This being the first.

Actually I was thinking of "Because." but I suppose that works too.