Suppose description of a website in page source is one and for directory submission it is different, is it helpful for seo of the website? Description should be same altogether. What is your opinion?
Yes, mix up your keywords, title, and descriptions when posting to directories. This will broaden the terms your site is associated with.
When doing directory submissions you should change your description as much as possible for best SEO results. Google like unique content and index it faster. Some directory submitters like DigiXMAS Directory Submitter can spin words in titles and description making the submission process much easier.
Yes, use different contents and descriptions for both. By this way you can include more keywords, which really helps in optimizing your website. Moreover, it helps in faster indexing also.