As I noted in the comments on Brett's blog, you get longer shutter speeds. Handy for a few things:
1. If you want longer exposures at a particular aperture. 2. If you want to shoot wide open on a bright day. 3. If you want to keep your shutter speed low for fill flash sync speeds (same as #1 for different purpose).
I seem to keep finding conflicting information, but it does seem that Canon provides less dynamic range at ISO 50 (see technical note here)
Quoted Message: have since heard it is good for snow pics. Could it be that its good for very bright pic?
See my link above - turns out it basically overexposes a stop and then dails the exposure back down post capture. This boosts the exposure in shadow areas for less noise, but can also clip highlights and drop dynamic range. So if you meter correctly (ie overexpose) for bright snow it probably won't help and may clip highlights. But if you let the meter expose white as grey and then boost exposure in post it will help as your shadows will have less noise. Or so it seems to me :)