Technically speaking, there are some differences between the title tags and the description sections of the html pages such as the way words and sentences are written as well as the way keyterms and the important business messages and slogans are going to appear. Both are important page elements and the search engines look for them while finding and crawling a new site. Some websites use a same title or description for many of the pages which is really not a good idea because the pages will look identical to each other in the eyes of the web portals and major search engines and some drops in listings might occur. You certainly will have more room and options while writing description lines for your web pages than the title tags because usually, as it's been seen on thousands and millions of the sites online, the title tags consist of a single text line while a description tag of a site may contain several lines of text messages and business slogans. Both are important in driving traffic and bringing in visitors to the main pages of the sites and while competing with other sites on the net.
If you have written a long text line and want to use it as the title tag of your web page, it probably might be a great idea clipping that and using the first part of it to serve as the title of your internet page and the rest of the sentence to go at the description section of your site. Please think of the ways of describing the contents of your site as well as the elements and ideas on your current pages while thinking of the text messages and words for being used at the title and description sections of your site. Sometimes, webmasters might prefer not using the description tags for their websites pages but using the titles for them is a must and web pages having not title sections are not called complete internet resources. A bad method of optimizing the pages of a site would be to write only a few words and then add them to the title and description sections of the sites. This is never recommended because although addition of the main keywords to the html tags of the sites is always great, but overdoing and stuffing them into the tags will be causing the opposite effect. You know, thinking of meaningful text lines for both the titles and descriptions is a great idea while building websites.