During an initial or cold start, CICS creates system tables by installing groups named in the list or lists named by the GRPLIST system initialization parameter. If you installed a group with the INSTALL command during the previous CICS execution, you must add its name to a list if you want it to be installed during a cold start.
If you usually use START=COLD at CICS initialization, installing by means of a list will probably be your standard way of making resource definitions available to CICS. Use of the INSTALL command is a supplementary method, which you could find very useful when testing a system, or if an unexpected need for a resource arises when CICS is running.
You may not want to use the RDO transactions in a production system, for security or performance reasons. In this case, the CSD file is shared by both systems, but is read-only in the production system. You define all your production resources using your development system, and install them in the production CICS system when you cold start it.