A title tag should:
1.       include keywords
2.       include words that identify the particular page’s content within the first three to five words.
Search Engine spiders consider approximately the first 60 characters of a title tag. They will easily identify keyword stuffing and it should always be avoided.
An example will help illustrate. Say you have a website that sells antique lamps. The title tag could be written as such:

Antique Lamps at Old Lamps Inc.

It’s very straightforward. The keywords are the first two words of the title tag. There’s a variation on the “lamps” keyword in the company’s name.  Some people make the mistake of stuffing keywords repeatedly into one title, thinking it will lead the search engines to thinking this page is more relevant to the particular keyword because it is repeated over and over. But this would be considered “keyword stuffing” and if anything, might lead to trouble, not to better ranking. Here is an example: 

Antique Lamps, Antique Lamp, Antique Lighting, Antique Lights, Antique Fixtures, Old Lamps Inc.

This title uses keyword stuffing.
It looks unprofessional  – it will appear like this in search engine results and will not appeal to consumers.
As you build your site and optimize it for the search engines, remember that the title tag can make a tremendous difference in both ranking and in searchers actually clicking on your entry in the SE results.