Manifest file necessary when packing an EJB jar resp. WAR ?

[Tobias Merler]

If I jar a couple of EJB classes together with the META-INF/ejb-jar.xml
automatically a manifest file is created and added.

Is this file necessary to be able to run the EJBs after deployment or can
I suppress the manifest generation?

Same question for Web Archives with target *.war

Tobias