Why have more than one VPAR on the system

Note: These apply to VPARs versions 4.x/5.x . For the latest in case of any differences refer to the latest documents on the VPARs

Why is this suggested to have more than one VPAR in an NPAR?

Addition of few resources as I/O and Memory do require the VPAR to be in down state.

If we have only one VPAR configured, we will be able to execute the vparmodify command keeping that VPAR down that is we will need to reboot the system in nPars mode if this is an integrity system or in an standalone mode when it is a PA-RISC system.