Uh yeah!
You can armlock the near arm or the far arm (far arm can be done by either spinning arm lock or, God I wish I knew the judo term for it, where you trap the arm against your neck/head and cup the elbow joint with your hands).
You can do neckcranks, cross collar chokes, the baseball choke (brutal choke), I know a shoulder crank from there off a takedown (one of those turning shoulder locks where you encircle the arm right at the elbow rather than figure fouring the arm)
There's lots you can do there, not to mention that it is a great transitional position as well. How else are you going to go from mount to side control and still keep everything tight?
Of course some guys don't like knee on belly and don't use it, but personally I use knee on belly and side control more than I use mount.