Possibly even worse that providing content with no meaning is marking up content with incorrect meaning.
Often used for indenting content. Should be used to contain quotations that are a paragraph or more in length - a block of a quote.
Often used for presentational layout. Should be used for tabular data only.
Sometimes used to indent content. Has a wide range of uses for items that have a direct relationship with each other (name/value sets). Should be careful not to use as a replacement when marking up tabular data.