Cache filter URL in Ecommerce Shopping site

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Girish Kapoor: Do we need to allow Google to cache filter URL in Ecommerce Shopping site ?
  
  One of my client which is an ecommerce website . i have a question that "do we need to allow google or other search engines to crawl the URL's which are generated after the users uses some filters to narrow down their product search on website". for example : if you are searching women shoes of size-7 from aldo brand shoes then you will filter by Brand and also by size then the URL genrated now is my concern do we need to allow to cache or index it or not.
  
  Thanks in advance. if you still didn't understand my question then please let me know
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  Federico Sasso: Regardless the filtering path used to reach a product page, every product page should leverage the canonical link to avoid duplicate content issues. If that is already taken care of, a search engine would only index the canonical URL version, not the ones generate by the filtering.
  
  Even then, for an e-commerce site crawlable faceted navigation can become easily an issue, with million of virtual URLs for the search engine to sort out, a serious waste of its crawl budget (which is: the limited amount of your site pages a search engine can crawl daily).
  
  So my personal answer is: no, avoid filtered/faceted crawling, only allow web spiders to reach your product pages using a well defined silo taxonomy (i.e. their canonical URLs).
  P.S.: XML Sitemaps often help in e-commerce sites.