JSPs are completely portable between different applications and different servers. This portability can be disadvantage because they have no particular application data knowledge.
Generic JSPs can be used for portable page elements, such as navigation bars or corporate headers and footers, which are meant to be included in other JSPs. You can create a library of reusable generic page elements to use throughout an application, or even among several applications.
For example, the minimal generic JSP is a static HTML page with no JSP-specific tag. A slightly less minimal JSP contains some Java code that operates on generic data, such as printing the date and time, or that makes a change to the page's structure based on a standard value set in the request object.