If you do, the browser will not understand the HTML tag and will ignore it. Be aware that your audience may be using different browsers to read your Web documents. Be aware of the strengths and limitations of the available browsers.
Many browsers display documents differently.
The latter would display correctly in Netscape but would cause problems in the Lynx browser. In particular,they may not work when the named anchor is inside something like an individual cell within a table. The browser may seem to take you to random places in your document if you ever try to make a link to it. It is easy to to make errors when inserting long URL addresses into your Web pages. Note that your Web pages will display fine on most computers without either of these tags.