Tag Libraries (TagLibs) define one or more custom tags that can be used to extend the capabilities of JSP. Judicious use of TagLibs can remove most, if not all, of the Java scriptlets from your Web pages. Encapsulating the Java code in a custom tag will
Simplify the writing of Web pages
Reduce development time by removing awkward Java compiler errors from the JSP-generated code
Integrate business logic constructs more closely into the JSP syntax
Custom tags can provide programming constructs, such as iteration and selection (if statements) for your Web pages. Custom tags can also
Use attributes to pass information from the Web page to the Java code
Create scripting variables that can be used on the Web page
Share information between tags ...