Modern (newer than ~10 years) modern controllers are quite flexible, so you can pretty much populate any number of DIMMs in any slots (apart from wrong ordering, though this is not a IMC restriction, rather firmware, for stability).
However. Disregarding the recommended populations usually means that the MC can't interleave the channels properly and also must choose other settings in a lowest-common denominator way. This severely reduces the performance of the memory subsystem, which includes cache coherency and all core communication in Zen.
Modern (newer than ~10 years) modern controllers are quite flexible, so you can pretty much populate any number of DIMMs in any slots (apart from wrong ordering, though this is not a IMC restriction, rather firmware, for stability).
However. Disregarding the recommended populations usually means that the MC can't interleave the channels properly and also must choose other settings in a lowest-common denominator way. This severely reduces the performance of the memory subsystem, which includes cache coherency and all core communication in Zen.