The HTML Small Element () makes the text font size one size smaller (for example, from large to medium, or from small to x-small) down to the browser"s minimum font size. In HTML5, this element is repurposed to represent side-comments and small print, including copyright and legal text, independent of its styled presentation.
According to Matt Cutts (lead of Google"s webspam team and the de facto expert on these things), using multiple tags is fine, as long as you"re not abusing it (like sticking your whole page in an and using CSS to style it back to normal size). That would likely have no effect, and might trigger a penalty, as it looks spammy. If you have multiple headings and it would be natural to use multiple "s, then go for it.
The HTML Element represents highlighted text, i.e., a run of text marked for reference purpose, due to its relevance in a particular context. For example it can be used in a page showing search results to highlight every instance of the searched for word.
