As Wadizzle said, some scenes have extreme dynamic range making it difficult to avoid blown highlights without losing details in the shadow area. Your choice depends upon whether the highlight or deep shadow detail is more important in the image.
Most cameras will provide the best dynamic range performance at their native ISO, 100 for all of the Canon models with which I am familiar.
In shooting sports, I often run into dynamic range issues especially in late afternoon where there is very strong side lighting of a scene. I shot a senior night softball game tonight which is typical of that sort of lighting situation. In the photo below, there are blown highlights but only in a reflection area on the batter's helmet and also part of the catcher's sunglasses and those aren't an issue. If those were important detail areas, I would have reduced the exposure.
I always shoot in RAW and that allows the best recovery from exposure issues in capture but if an important detail area was completely blown then even RAW adjustment won't be sufficient because once the light levels are beyond clipping in the A/D converter the detail data is gone. Canon's RAW converter will also create an odd color shift with 1DX III files when there is a severe blown highlight issue.
Rodger
