Usually, I\'ve seen it with forms, but I\'ve found it helpful to group related sets of data (eg when you have multiple tables on a page, using a fieldset around each table o
If you want to group tables, consider using an appropriate heading (h1-h6) element for each group. Individual tables can be described using the 'caption' element. The 'summary' attribute is also available for each table.
From the spec:
Each table may have an associated caption (see the CAPTION element) that provides a short description of the table's purpose. A longer description may also be provided (via the summary attribute) for the benefit of people using speech or Braille-based user agents.
And for the record, the 'fieldset' element is not intended to be use outside of forms. And within forms, it is intended to conceptually group like input fields - things like 'personal information' or 'billing address', etc.
Here's an interesting article that discusses what screen-reader users hear when navigating fieldsets. http://www.rnib.org.uk/wacblog/articles/too-much-accessibility/too-much-accessibility-fieldset-legends/