You find the same information in note 1749142 - How to remove unused clients including client 001 and 066
Introduction
You have to secure any client even if it is not used. This includes the security settings of standard users like SAP* or DDIC or EARLYWATCH which might still have well-known standard passwords as well as the security of any other (powerful) users.
Because of this you can reduce maintenance effort and increase the security of a system if you remove unused clients.
Client 001 is a copy of client 000 which was created during installation of the system which might have happened years ago. This client could have been used to become the productive client. However, if you have decided to use other clients as productive clients but not client 001, then you can safely remove the client 001.
Keep in mind, that a SAP Solution Manager System or a SAP Business Warehouse system usually uses client 001 as a productive client.
Client 066 is a client which was created during installation of the system (applicable for all SAP systems based on SAP NetWeaver 7.40 and below), which might have happened years ago. This client had been used to deliver services by SAP Active Global Support. This client is not used anymore, therefore you can safely remove the client 066. (Note 7312 shows some more information about this client and how to (re)-create it in case you want to get it back after deleting it.) SAP NetWeaver 7.40 is the last release delivering the client 066 with the installation or upgrade.
Caution: You must to NOT re-create this client as customer client in order to ensure smooth change control and maintenance processes in your SAP system.
This blog explains how to delete unused clients including client 001 (if not used) or 066 (which is not used anymore).
Prerequisites
It might be necessary to set profile parameter login/no_automatic_user_sapstar = 0 to be able to logon using built-in user SAP*.
You might need to implement note 2284180 to change the role of client 066 to TEST.
Caution:
Prior to deleting a client - especially in case of client 001 - SAP recommends checking if there are in fact no active users in the client. You can use report RSUSR200 of the User Information System (transaction SUIM) or the Workload Statistics (transaction ST03N) to check if there have happened some activities of users. Within ST03N you can use the Analysis View "Settlement Statistics" to inspect which clients had been used and which users have been used these clients.
You can lock all users (except one user of course) for some time before delete the client.
In addition you should check if no background job is scheduled within this client. You can easily check this using transaction SE16 for table TBTCO or view V_OP with a selection for the client using selection field AUTHCKMAN.
By the way: Getting the user name which executes a job step is more difficult: This information is stored in another table TBTCP in field AUTHCKNAM. To get client and user together you need to join both tables TBTCO (containing the client) and TBTCP (containing the user).
Finally you have to ensure that the client is not classified as "productive". Use transaction SCC4 to check and maintain the client role.
If you are going to delete a client which had been used productively formerly then you should check note 934593 which describes how to delete all objects of a client from TemSe (this part is not covered by transaction SCC5).
Do it
You can remove a complete client using transaction SCC5. You have to logon to the client which you plan to delete. On the selection screen of SCC5 activate the option to remove the entry in table T000! Use the background mode to delete a large client like client 001. (This is not required for the small client 066.) The transaction offers a test-run mode, too.
To monitor the progress of the client deletion, use transaction SCC3.
Finally you should check using transaction SCC4 that there is no entry for the client in table T000 anymore and you should submit report RSUSR003 to check if no access to this client using standard user SAP* is possible anymore.
References
The notes 70643, and 365304 (which is quite useful if you delete a large client) and 446485 (which is about copying clients but gives recommendations for deletion as well) describe some more details about the client deletion process. Note 31496 describes options to recover a deleted client.
Online Help - Deleting Clients
http://help.sap.com/saphelp_nw70ehp3/helpdata/en/4d/7cdfbc19a00f88e10000000a42189b/frameset.htm
Known issues:
Specific versions of the upgrade tools check for the existence of client 066 and stop the upgrade if this client does not exist. In this case simply create the entry for client 066 in table T000 using transaction SCC4 again, restart the upgrade and remove the entry after the upgrade again.
See KBA Note 1874687 Error in SUM phase EWIMPORT_UPG
Software Update Manager 1.0 SP13 will not request for a client 066 any more.
Post Processing
Set profile parameter login/no_automatic_user_sapstar = 1 for all application servers to block built-in user SAP*.
Consider to reorganize the database if you have deleted a large client. Search for notes about 'reorganization' within the application component of your database (e.g. BC-DB-DB*, BC-DB-HDB, BC-DB-INF, BC-DB-MSS, BC-DB-ORA, BC-DB-SDB).
Here are some references for Oracle:
