In technical articles it is sometimes convenient to place a table of contents on the first page, right after the title and abstract. I find the section entries in the default table of contents for the article style to be too assertive and too widely spaced for this purpose. The command
\tighttocproduces a tighter table of contents. It was used to generate the table of contents on the first page.
You will probably not want to use \tighttoc in the report
style.