I put a much more detailed answer in a similar question here:
http://gaming.stackexchange.com/a/106909/28378
But basically digital signals add extra processing delay, and HDMI is digital. For video and a decent TV, this isn't a big deal unless you've got the TV configured to clean up/change the video. Turn that stuff off, but stick with HDMI for video if possible and stomach the small extra video delay.
For audio, you're adding a whole extra "middle-man" (your TV) to the mix, which is very bad.
If you're wanting audio going to your external receiver/speaker system, passing it through the TV just means the TV has to split it from the HDMI video and churn it back out its audio out connection, which usually takes a long time for a TV's budget audio circuitry. Instead, use the optical out from your PS3 to the receiver.
If you're using TV speakers you're out of luck for decent sound anyway. Go ahead and use component cables in this case so at least the TV isn't doing the slow digital-to-analog conversion.