What's LVP?

Can anyone describe me that what is the difference in high voltage and low voltage programming...& when is either of them choosen??

If LVP is enabled, PGM pin cannot be used as I/O anymore. This is the trade off.

A high voltage (around 12-14V) on the MCLR pin, this is called HVP (High Voltage Programming)
LVP (PGM = 1) as it suggests you don't need the higher voltage to program the disadvantage is that you loose one pin.

I never use LVP mode I use HVP all the time.