Serial presence detect (SPD) is a standardized way to automatically access information about a computer memory module. Memory generally comes with conservative timing recommendations in the SPD. So by leaving everything on AUTO you don't get rated memory specifications you get conservative SPD settings.
Extreme Memory Profile (XMP)
A similar, Intel-developed JEDEC SPD extension for DIMMs. This uses bytes which are unallocated by JEDEC to encode higher-performance memory timings. The higher-performance memory timings are the rated specs for the memory.
XMP automatically sets DRAM Timings, DRAM Voltage, and Memory Clock to rated specifications. You can also enter these settings manually. Please note that XMP settings are by default DISABLED.
BIOS settings:
MB Intelligent Tweaker(M.I.T.)
Extreme Memory Profile (X.M.P.)
Allows the BIOS to read the SPD data on XMP memory module(s) to enhance memory performance when enabled.
Disabled Disables this function. (Default)
Profile1 Uses Profile 1 settings.
Profile2 Uses Profile 2 settings