What if it's a wader for instance , I assume it would have to be the right distance away ? This has baffled me for a while. With the zoom you just pull back or extend with the lens.
Fact of the matter is, you usually can't get close enough so you end up cropping to get the final composition. If the target gets too close then you simply have to switch to head shots, or change the lens!
I'll be off to Slimbridge soon ,it's a Wildfowl Wetlands Trust place and I'll see how I get on with what I've got ,my neighboour's coming with me and we'll see how effective the 70-200 is.
It's only with this f2.8 IS that you are able to leave the IS on but as you say the norm. is to switch it off.