ETTR is not 'overexposing', it is giving 'just a touch more exposure' so as to better allocate the usage of bits, so that more show detail can be extracted yet not lose an highlight detail. It is part of a somewhat broad definition of 'proper exposure'.
Of the real 'overexposure' vs. 'underexposure' which is better to do?, forget the theory
and look at a specific, practical example of what happens with each error (vs. 'proper' exposure.)
Just shot the following three shots (at 0EV, and -2EV and +2EV exposure).
- the 'underexposed one is boosted +2EV in post processing
- while the 'overexposed' one is reduced -2EV in post processing
in Lightroom. Look at the detail in the white flower petals, and look at apparent noise in the three highly cropped sections...
Correct exposure (1):
Underexposed (2):
Overexposed (3)
The detail in the petals is totally missing from the overexposed shot (3), and the noise is increased in the underexposed shot (2) especially noticeable in the flower pots.
- I can run noise reduction (not yet any NR applied to shots) to decrease the noise seen in #2.
- I cannot do anything to restore data lost in clipping my data (falling off the histogram in the eternal bit bucket)
I am probably a product of the film era concept in photojournalism, 'Get the shot!'...'Tis better to get a noisy shot than no usable detail in the photo.
If my mission was to document the winner of the flower show (white flowers) I failed miserably to document the beauty of the white petals and get a shot of them, if #3 was my only shot!!!
In the noise of offset printer dots, the reader probably would not much notice photo #2 noise, and my editor would be satisfied!
If I brought back #1, he would pat me on the back and express his gratitude for not disappointing the Flower and Garden editor!