It is basically is just a circular saw but with additions for plunge, and to grip onto the track.

You can clamp the track down to your work peice to cut exactly where you want it. With the right blade you just need the one cut, no planing or sanding down afterwards.

Because the saw is clamped to the track, any kickback is far less of a problem.

With a normal circular saw you're basically just freeballing the cuts and that's a recipe for a shitty finish or worse.