If you’re going to think about how the system works, it seems worthwhile to think about it correctly. Per MIPS:

Think about a fall on a slippery slope: If you fall and hit your head (or helmet), you will most likely continue in the same direction as before the fall. Alternatively, consider a similar fall on high-friction asphalt– a very different scenario. When your helmet hits the ground, there will most likely be a sudden stop and a rotation of the helmet. Mips® safety system intends to redirect that energy away from the head.

In summary, the difference between a helmet with and without a Mips® safety system is that a Mips® safety system allows the helmet to move 10-15mm relative to the head on certain angled impacts.

There’s lots of good info on the MIPS site: https://mipsprotection.com/science-technology/