I was asking myself that question earlier in my head after reading a different thread on Cokins and holders.
one thing that i thought of is that if your sky is really bright, and your subject is really dark, you can either:
- expose the sky to just below full-blowout, and boost the brightness of the dark bits in Post Processing (less detail though).
- expose the dark bits nicely, but once the sky's blown out to full white, no PP can get any detail back.
- bracket exposures and combine them in PP (never done it, but i presume it'll take a bit of time)
- grad-nd will expose the dark bits nicely, stop the sky from blowing out, but my guess is that it works best only on straight-line horizons? what if you've got a mountain peak or two?