Stef (or was it Ingix??) gave a sentence about it, in the overview of this major change; but I have to admit that my limited brain function leaves me still confused.
Can someone explain? Maybe give one or two examples, if that would be easy to do. I expect (hope??) that I'm not the only one confused by this particular update/change. :)
It means when you play a Village and watch the animation of what it does, you can already click on the Smithy in your hand to play that afterwards.
Generally it means when you next need (or whant to) to select a card, but animations are running for something else, you can click on the card, then it's used when the click is "needed".
Another example would be buying the last 2 Provinces: While the first one is moving to your discard pile, you can already click on the last one.