What is the difference between MCLR and switching VDD OFF-ON?

[amgen]

one thing that can happen is if you have any +5 volt on any of the peripheral pins, the input to the pins inside the PIC have diodes pointing to the supply voltage and then that 'could' keep the pic from resetting..... then, I don't know what..... maybe back to software instruction to reset....@RESET. Or if you take away/turn off power, would have to turn off the power for all external parts