I generally have a tendency to underexpose images to avoid white clipping, especially when doing landscapes so that the sky doesn't get ruined as white clipping looks worse than black clipping. I know you can get use Lightroom tools to recover areas but I aim for the best shot when I'm taking it.
However I just read a book on Camera Raw ('Getting started with Camera Raw' by Ben Long - 2008) which explains you should lead towards overexposure rather than underexposure because the way cameras allocate bits towards capturing brightest is skewed towards the brightest part of the image. And therefore it has more data to play with when making adjustments in the brighter parts of the image than the darker.
Is this still true?
And why does it do this way rather proportionally the same for lights and darks? (The book didn't explain this).