It may not do active harm, but it can't possibly benefit either the page or the site. Either make page-specific descriptions-- assuming that's what you mean by "meta tags"-- or omit them entirely. Obviously some metas will be the same on all pages-- "viewport" is the obvious example, or "charset"-- but that doesn't sound like what you are asking about.

I am asking only about title, description meta tags

Hi vijaykumarcirigimi and welcome to the forums. Every page should have a unique title and description. It is a basic "good practice" of site creation. Do you have a Google Webmaster Tools account? You will be able to see a section called HTML Improvements listed under Search Appearance in the menu on the left side of the page. There you can see the recommendations they might have for your site. As for "what happens?" - you may find that Google is substituting their own ideas gathered from your pages instead of the titles and descriptions they find there. They specifically mention those two areas of pages as possible problems:

Title problems: Potential problems with the title tag on your pages, such as missing or repeated page titles.
Meta description problems: Potential problems with duplicate or otherwise problematic meta descriptions.

If you have separate content for your mobile site and desktop site, Google recommends that you use bidirectional link annotations to indicate the relationship between the two URLs for search engines.