The frame rating tells you the physical size and the maximum continuous current the breaker's thermal-magnetic trip system can handle — here, the 600 Amp frame gives headroom above the 500A rating, which means the breaker is not running at the thermal limit of its mechanism. For a panel builder, that translates to better long-term reliability and less nuisance tripping from ambient heat buildup inside the enclosure.
Deployment context
The 600 Amp frame size means it occupies a standard three-pole mounting footprint common across the LE frame family, so retrofitting an existing panel layout should not require re-drilling the backplate.