Unfortunately this ONLY fixes such a problem for Google and NOT other search engines. IMO using Google's WMT prefered domain (www vs. non-www) setting and the parameter omission feature are a bad idea. Canonicalization issues affect all search engines, and using prioprietary fixes in Google WMT only fixes it for Google.
You are much better off using 301 redirects to fix www vs non-www canonicalization issues and avoid the use of querystring parameters (implement search engine friendly URLs instead) to fix the parameters issue. Querystring parameters are a deathnail in any site's SEO and should be avoided at all costs IMO.
I suppose if you don't know how to implement 301 redirects and how to implement search engine friendly URLs (avoiding querystring parameters) then it's better than nothing... but if you can't come up with a better solution than Google's WMT to fix these types of issues, you're not much of a webmaster/SEO.