This is the legacy way to configure VTP client mode. VTP client mode doesn’t allow to create any VLANs. All VLANs must be learned from a server switch. This prevents the switch from accidently propogating VLANs throughout the network. The other use for this command is to prevent an older switch from wiping out a server’s VLAN database due to it having a higher revision number.
In the below example we will set SW1 to be a VTP client and add a VLAN to it. Notice the switch rejected the command because it was in VTP client mode at the time.