Well on newer motherboards that deal with a lot. The updates can fix small issues with certain CPUs, improve RAM compatibility and supported speeds. Support newer CPUs released on same chips etc and other improvements.
This is what changed on the most recent bios for my motherboard.
Quote:
"1. Include Turbo Game Mode: Enhance performance in certain games.
2. Update AGESA Version to Combo AM5 PI 1.2.0.2a: Enhance compatibility and performance
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and a previous one
Quote:
1. Update AGESA version to Combo AM5 PI 1.0.0.7.a
2. Support 48/24GB high-density DDR5 memory module.
3. Memory QVL amended to account for AMD 1.3V SoC voltage limit.
4. EXPO/XMP prompt notice removed.
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So it varies a lot. Sometimes simply improvements to stability etc. When AM5 for AMD first released RAM compatibility was bad and the speed it safely worked at was not great. There was also a lot of issues around running 4 sticks of DDR5 rather than 2.