In a nutshell, you can adjust the fan curve for your system to be dead silent under low loads, but can ramp up the fans very high during intense gaming when things heat up. And when you find a sweet spot, that's what you'll keep basically forever, it's fully automated from then on. You can also define what's the temperature sensor used for the fan curve. It can either be CPU based and quickly responds to temperature differences or you can set it to be based on motherboard temperature (case air temperature) which responds slower and ensures certain ambient temperatures. Fan can fluctuate a lot more with CPU based which can be annoying sometimes if you can hear fan ramping up during 100% CPU load, but instantly falling down as soon as load drops. With other sensor, fans will raise slower and also run at that speed for longer even when CPU doesn't have the load anymore as the temperature in case will still remain for a while. It's up to you then to decide which mode you prefer. Main difference is, with CPU based, you're "carving" the fan curve at higher temperatures (even up to 85°C) on the graph where with ambient you'll probably want them below 50°C as having this hot air inside the case, it means something is emitting quite a lot of heat.
Btw, one really annoying thing with ASUS is that on every BIOS update, ALL settings get erased, even stored (saved) settings, which include fan curves as well. I had to write each down before updating BIOS and because I had quite complex setup, it was quite annoying. My MSI already came with latest BIOS so I'm not sure how it behaves in this regard... Settings profiles are certainly more flexible and easier to use on MSI than on ASUS, so it's likely they store it separately...
