First of all, what are ‘tags’?
Tags are a set of words or phrases that are attributed to a blog post (or other object such as an image) by making it easier to find by grouping the blog post with other pages of associated content.
These tags help users to conduct research in the field that they are interested in by helping them to easily source other associated information. Tags also assist search engines with determining page relevancy.
So what is a tag cloud?
A tag cloud is basically a weighted list of tags. The tags within the tag cloud are given this weighting via a larger or smaller font size. This allows the user to easily establish which tag category is the most popular and allows search engines to better determine the amount of focus from the website to a particular market segment.
This should therefore in theory aid your appeal to search engines for your more popular tags.