Using Catalyst as a video switcher is certainly possible but not always a great idea. If you are doing purely IMAG then Catalyst switching is not a good idea. If however you like lots of visual and color effects with your inputs then Catalyst is a good choice.

Something to mention also is that Catalyst can control matrix routers. I have configured systems to use a 16x16 matrix router feeding 4 HD-SDI inputs on two Phoenix Cards. The 4 inputs then act as sort of a 2 M.E. Switcher.

You are going to notice drop frames and you will see a latency of about 3 to 4 frames alone just in Catalyst.

If you remain SD and are fine with composite sources, you can run three LFG4 Cards in a Catalyst for 12 total mixes. You will still notice latency but my observations are that the LFG4 is faster than the Phoenix by a few frames.