I need to save myself the hassle of switching b/w onboard sound and sound card when enabling/diabling them so I set Control Panel default playback device be my sound card and I set default recording device be my onboard sound. It seems to be working and I need to know what the down sides are to this?

Explanation of why, if needed, is this:
With stable earlier versions of ATi Multimedia Center, there is an echo if using 5.1 or newer sound cards. Echo can be manually adjusted each time using sound card software Line-In settings, however input volume cannot be adjusted if using newer sound cards. It resets back every time recording starts. This is a known ATi MMC problem. I can take care of this problem by either using an older 2.1 sound card or by temporarily disabling newer sound card and using onboard audio while capturing.

Why not enable both onboard and sound card and set each for just playback and just recording?