[Rover]

It is very simple. That you have the ABILITY to use more shallow DOF gives you more creative potential than when that ability is non-existant. Why? Because when you don't have that ability, that option is not there. Same as with FOV. If you only can shoot with a 45 degree FOV, you have less creative potential than when you have for instance 125 to 10 degree to work with.

 

That does not mean that you have to shoot with shallow DOF all the time. Just means you have the potential to do so.

Am I the only one to think that the issue is way overblown anyway? I have to admit I'm shooting only 1.3x and 1.6x crop cameras but even on 1.3 the DOF is a constant headache even at medium apertures (like f/5.6) when using a f/2.8 telezoom. Shoot anything even somewhat 3-dimensional or angular to the focus plane, and you run into issues. I was sifting through old pictures a few days ago and ran into a bunch of examples with large areas being OOF. Or there was a lizard picture shot from above, almost parallel to the body - all of the critter in focus EXCEPT for the (slightly raised) head which was totally OOF despite the aperture presumably being nowhere near wide open (since it was a sunny day).

Now, if you need some extreme situation - like shooting full body portrait with normal to wide lens, and wanting to separate it from a not-too-distant background - then, of course, you'd be clutching at every straw. But remember that this lens - the 40-150 that started this thread - is a journalistic telezoom (in fact, a pal of mine who works for the country's foremost agency is using this lens on an Olympus OMD body alongside 1DX), and for journalistic use, more DOF is usually better, not less.