I think that ETTR should be defined as "increase exposure until you have objectional highlight clipping, or objectional motion blur or objectional lack of DOF". In other words: expose hot, but not too hot and not if it makes the image look bad. Then motion blur should not be a problem either?
This is how I think of it:
In circumstances where:
- There is no undesired motion, from either camera or subject, that a longer exposure would exacerbate.
- There is no localized veiling glare
- Highlights are controlled
- You're using an ugly-noise camera
- You want to spend time correcting the exposure later
ETTR may provide a slight benefit in numbers. Even then, I have doubts as to whether this is visible on screen or in print.
In the real world of photography and not lab tests, some or all of these criteria are not met. Plus, you'd need a stout tripod, mirror lockup and a remote release to eliminate all vibration to eliminate any pixel-level blurring. Obviously, with a lot of subject matter this just isn't practical.