XMP: What is it, and should I use it?

[Harbinger35]

I have 4GB DDR3 memory (4GBRH), and I have the option for XMP: Should I turn it on, or leave it off?

Gigabyte P55A-UD3
4GB DDR3 memory
GTX 460 1GB
Intel Core-i5 760

Thanks.

[GSKILL TECH]

Turn it on, that uses the best settings of the memory. If turned off, you have to manually set them.

Thank you
GSKILL TECH