If your site has a lot of pages and especially if its an ecommerce web site one of the really quick and legit gains you can make in the SERPS is by addressing the duplicate page titles you may have on your site.
Why are duplicate page titles bad?
Page titles still remain ‘the’ most important on-page element in helping to rank for specific phrases so having a whole bunch of page titles that are duplicate, and worse – not even representative of the page content/product is a really wasted opportunity. Unique and descriptive page titles should be one of your SEO priorities. Ensuring all your page titles are unique and represent the page content is a major step to maximising the number of pages on your site that can rank well for a wide variety of terms.