Most examples I\'ve seen have scripts in a html page being enclosed by
I\'ve tried writing it without the comment tags a
Really old browsers that didn't understand the tag might assume that it was a formatting tag it didn't understand. They would gracefully fail by rendering the contents of the tag (the script) inline in the page.
By HTML-commenting out the script too those browsers will ignore the content rather than rendering it.
In practice I doubt any of those browsers are still in use and that you can probably get away without the comments nowadays.