Intel XMP or AMD EXPO are memory profiles containing information about RAM frequency, latency, voltage, and more, and are meant to instruct your motherboard on which settings to use. Many users know that enabling XMP/EXPO in the BIOS/UEFI is necessary to run the memory at the advertised speed and latency. However, what is probably not as obvious is why manufacturers don't enable these settings by default, considering most users will almost always enable them afterward.
There are a couple of reasons why this happens, and they all have to do with system stability. Enabling XMP/EXPO by default would be more trouble than it's worth, and hence, it's better to leave the decision to individual users.
If you haven't enabled XMP in your BIOS, you're leaving performance on the table
Your motherboard doesn't enable XMP or EXPO by default, so make sure you enable it for peak performance
Manufacturers want to avoid a deluge of support requests
Playing it safe
Not every PC user knows about Intel XMP or AMD EXPO settings. A large section of users still buys pre-built gaming PCs, and doesn't want anything to do with messing with BIOS/UEFI settings or optimizing their PC for gaming. They're expecting a machine that just works — plug and play. If manufacturers found a way to enable XMP/EXPO settings before their motherboards ended up in gaming PCs, thousands of users would be left with bricked systems.
The tricky thing with XMP/EXPO is that it isn't super seamless. You can never guarantee that a particular PC will boot with a specific memory profile. Uninformed users will be stuck with boot loops or cryptic BIOS/UEFI screens, not knowing what to make of either. They wouldn't know about turning XMP/EXPO off in the BIOS, or experimenting with an alternate profile. The first thing they would do is call the vendor they bought the PC from, and rant about their brand-new machine not working.
Manufacturers want to avoid these situations, and hence, leave the memory frequencies at the default JEDEC values. This is 2,133MT/s for DDR4 RAM, and 4,800MT/s for DDR5 RAM. If you remember entering the BIOS/UEFI for the first time on your most recent build, you would have found your RAM running at these speeds, depending on the generation of your memory kit. Leaving the RAM settings on the default values sacrifices performance, but it ensures the system will POST successfully.
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XMP/EXPO isn't stable across all systems
Giving users the best chance
XMP/EXPO ensures you're making the most of your memory kit, but it isn't a fool-proof standard if you consider the myriad of hardware combinations possible on PC. The CPU, motherboard, and RAM need to work together to ensure stable functioning at a particular memory profile. If the CPU's memory controller isn't capable of supporting the XMP/EXPO settings in question, or the motherboard's QVL (Qualified Vendors List) states that your RAM is too fast to be supported, you're all out of luck.
In such cases, enabling XMP/EXPO by default might or might not result in a successful boot, but even if the system seems stable for a while, it might not stay that way. Crashes during games or other programs, blue screens out of nowhere, and overall system instability are the reasons why using the default JEDEC settings is the best bet. The users who know about XMP/EXPO will enable it in a few clicks; those who don't care will get a stable system without changing any settings.
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XMP/EXPO is technically overclocking, and cannot be the default
Not exactly the best precedent
Finally, enabling XMP/EXPO isn't, and shouldn't, be the default because it is nothing but overclocking the RAM. Unlike manual overclocking, where you tweak the frequency, voltage, and timings yourself, XMP/EXPO are templates that automatically overclock the RAM with settings that the manufacturers have confirmed to work. That said, the chances of success of these profiles working as intended depend on a lot of factors.
Not all memory configurations will work with XMP/EXPO even if your motherboard and CPU support it. For instance, populating all 4 RAM slots with high-speed RAM (even 6,000MT/s DIMMs) almost never supports the maximum-rated speed of the RAM. You will be forced to set a profile with a slower frequency or use the default 4,800MT/s for a stable system. Other times, you might have to manually loosen the RAM timings to make a particular profile work successfully.
These inherent challenges with overclocking the RAM are the reason manufacturers can't simply enable XMP/EXPO by default and hope for the best. Just like overclocking the CPU or GPU is fundamentally risky, using XMP/EXPO has its challenges around stability. Manufacturers can't officially enable something that technically overclocks the memory.
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Never forget to enable XMP/EXPO
As a reader of XDA, you likely know about the importance of XMP/EXPO already. On the other hand, if you came across this article, and realized you never enabled XMP/EXPO on your PC, now is the time to do it. If your CPU and motherboard support your RAM's rated speed, it's best to enable the corresponding profile in the BIOS/UEFI. Overclocking your memory beyond its rated frequency and latency is something you can experiment with, once you're confident that you know what you're doing.