Mainly making you aware of things like Density Altitude and flight planning, mountain weather, showing you little tips like experimenting with climb power on downwind to make sure you'll actually climb on take off, leaning for best power on the ground, choosing abort points that "if not off by....." etc.... For Catalina it was just some circuits on the airfield, which in itself is not that difficult. The thing is it is a bit of a carrier deck (google image search Catalina Airport) so if you come in low/slow you could be in trouble, and you get some pretty strong updrafts at the end of the runway. Equally when you take off the runway is a bit humped so you think you're going to drive right off the edge of the cliff - but you're not, the runway is huge at 3000' -I suppose they don't want you to do anything stupid...