If you don't add a description tag, what will happen?
That's right - the search engine will use the site's text as description.
If your site does not contain any clutter, you therefore don't need a description tag.
Also, consider this:
if you add a description, and if Google accepts it, it will always show underneath the link in the SERPs.
If you don't add a description, Google will choose the part of the page with the relevant keywords and show it to the user in the SERPs.
