Why we need to go for ejb rather than JSP and Servlets?
Without knowing the specifics of your project, it would not be possible to offer a suggestion.
If you really think that the classes/objects that you have identified during your design will never be re-used by anyone in a big way, ... use servlet and jsp.
But when you develop some applications ex. Banking and you expect that certain components may be useful for you or anybody else, better to use EJB or any other component based architecture
reuse is a good thing, but EJB is not just about reuse. Because you can manage to reuse regular java classes (as well as servlets too) if you write them correctly.
EJB has other advantages:
any transactional sessions should be handled by EJBs.
EJBs promote the multi-tier model much better (such as MVC aka model 2).
this is a start, but like said above depends on the project.