There is a possible problem when bringing new switches onto a network. If the new switch is configured with the same VTP domain name and the same VTP password, it is possible it could erase all the VLAN configuration for all VTP domain Server and Client switches already existing on the network. It will only happen if the new switches revision number is higher than that of the VTP domain switch servers revision number.
To Avoid this do one the following:
Configure the new switch for VTP transparent mode and then once added to the network switch it to VTP client or server, this will reset the revision number to zero making it impossible to overwrite vlan data.
Erase the new switches vlan.dat file, which will also reset the revision number to zero.