Okay, normal capture cards are NOT meant for recording of live gameplay. They're meant to record stuff off of TV and DVD players and camcorders and stuff. Stuff where it doesn't matter if there's lag between when you press a button and when the action happens on the screen (like changing the channel with modern cable).
However with video games, if there's lag between when you press a button and when you see the action, you're generally going to suck, die, and not have any fun and end up with nothing more than a recording of you failing terribly at the game...
This is because cards spruce up the video a bit (in various ways) for displaying and recording (and modifying live) on your computer. Well, some cards have a "game" mode, meant for playing games. This turns off the extra features and such so that the game can just stream to your screen without the delays. This lets you actually play them properly.
It's sort of like the "clean" mode some flash carts do that will bypass new AP, at the cost of cheats and soft-reset.
