Why, oh why?? Now I get it if one wants to stay in a hide all day, or if you otherwise park yourself in one spot AND you're shooting with an older camera with poor high-ISO capabilities AND the light is poor, but otherwise you're far better off with a crop-sensor camera like a Nikon 1 and 70-200 f2.8 lens.
For wildlife photos, you've really got two ways of shooting: get to the subject, or pray it will come to you. One way requires a big lens like this one, and the other requires portability. Since my pockets aren't deep and I can think of better ways to get a workout, I'll stick to the bigger-is-not-better routine.