My partner uses a 7D and 5D2. He usually has the 24-70mm on the 5D2 and the 70-200mm on the 7D. I use two identical bodies though.
Sure, you get more magnification using a crop sensor. But the safety of having an identical body outweighs that advantage. What if the full frame stops working, even for just five minutes? And don't discount the difficulty of switching between two sets of controls. When things are happening quickly, every millisecond counts.
And regarding the benefit of a lens being two different angles of view on a crop and full frame, if you really need those different angles of view, just use a zoom. Or have two primes with those focal lengths.
Well, everybody has their opinion on what is an advantage, and what isn't. Having an identical body is definitely not seen as an advantage to me. When I shot just full frame, I carried around a 135. Now with a crop, I have dropped the 135 from my setup completely. That is better than having an additional lens in the bag IMO. I've even considered getting a 300mm because 200mm on full frame REALLY isn't that long. You gotta be pretty darn close to get a half or third length shot for reception shooting. But 200mm on a crop solved that for me. Now I don't feel like I am obstructing anyone's view as I can shoot much further back.
Also, I just like the look of my primes on crop better than FF. The DOF is just too damn narrow on FF. Sure I can stop down, but bokeh is ALWAYS nicest wide open. A lens' given character is always described from it's wide open character. Crop gives me just enough DOF, and the most pleasing look of being wide open. Great when you have more than one person in the picture (like a wedding).
I shot FF exclusively for 15 years (film). I was THRILLED to suddenly have another option. It really opened a lot of creative and logistical doors for me. In the end, it's all about what advantages speak to you. For some, it's FF all the way, and for me, crop will always have my heart. I'd rather lose my FF body than my crop.