Can anyone explain what Xcomposite extension and Compositing manager are and do?

What hardware are the two elements related to? Running in Slackware12 w/Lcdmonitor sxga+ no interlacing 1600x1200 @60hz and AGP x2 ATI 32mb video card

Is the xfwm4: warning display doesnt support xcomposite ext
referring to incompatible hardware or configuration error?