Title Tags are one of the most important elements of an optimized website.
A Title Tag tells the search engine what your page content is about which helps it deliver the right page to a searcher. It should be unique and keyword focused.
Duplicate Title Tags (tags that appear on more than one page of your site) tell the search engine that the pages are of low value, not important enough to merit a unique tag. Duplicate tags may cause the search engine to filter your pages and not deliver them and deny them the ability to rank for key terms.
For optimal local search results, the Title Tag should also incorporate a geographic attribute (city, or ZIP Code).
A Title Tag can not exceed 66 characters. You can tell the Title Tag is too long if it is displaying with an ellipse ( … ) at the end of the text. The Moz.com website has an excellent Tutorial on Title Tags.
There are many Title Tag testers, Google it and you will see many options. Here is an example.
To understand the importance of Title Tags read out blog.