This is one of those Basic SEO posts, that i feel silly writing about because "everybody knows" this information already. But then I look at websites of prospects and I realize that not everybody really does know. Or maybe they do and they just forget. In any case, this will be a quick reminder / refresher.
Most duplicate content issues have to do with on-page content. Mass page/content duplication can often have a negative effect on how the search engines spider and index your site. While I believe the title tag is the single most important piece of real estate on your site, duplication here is likely to have the least effect on the search engine crawlers. Even still, it's a duplicate issue that absolutely must be addressed for tactical SEO performance.
Duplicate titles is something we often see on newly developed websites or content management systems that don't allow proper control of individual pages. While I get how, when developing new websites, the title tag can get overlooked, I'm still amazed that many internet savvy software developers still don't take title tag customization into account.
In some cases it's just a matter of some creative programming to fix. In others it might require some significant reworking of the system, or a scraping of the system altogether. And, of course, other times it's just a matter of taking the time to get into your HTML or your CMS and writing unique title tags for all your products and content pages. If you have a lot of products or pages, this can be time consuming, but it's well worth the effort.
If you can pull it off with your CMS, allow Titles to be automatically generated based on on-page criteria, but also give yourself the opportunity to overwrite the defaults with your own customization. This is especially handy for product pages. The default can display essentially the breadcrumb trail of categories down to the products as the default. This will ensure all your title tags are unique, to a degree. But at some point you may want to get in and create a unique title tag for more punch and better search engine rankings. Having both options will give you the greatest degree of control without having duplicate titles until you get around to customizing them.
Do whatever you need to do to make your title tags unique. And by unique, I mean, not tied to any other element on the web page such as the header or breadcrumb trail.
Having unique titles on every page is great, but not if they are always identical to the your page's headers and breadcrumbs. This just creates a different form of duplication.
There are some cases when it makes sense to have your Title tag and H1 tag in very close alignment. Typically this is done in blogs or other informational articles. But I still recommend keeping an element of control that will allow you to change them to be unique whenever it makes sense to do so.
All said and done, your titles should:
* Short, 65 characters max
* Unique for each page
* Accurately reflects page content
* Contains main keywords