The use of Pragmas is disputed or ignored by many. But there is really no reason to not consider what a pragma directive actually does and how it can help you relieve performance pressure on your web site.
In the old days, pragmas were used to give specific instructions to browsers. These days browsers are smarter and many directives may be unnecessary.
Pragmas may appear in ASP(X) pages to be handled by the web server, or embedded in the HTML to be processed by the browser.
When optimizing web sites for better performance, it may be unavoidable to dive into pragmas.