This page is for the Fabric version. If you are looking for the Forge version you can find it here.
This mod reduces the memory usage of Minecraft in a few different ways. A high-level technical description of the changes is available here.
The amount of memory saved will depend on the pack. In version 2.5.9 of All Of Fabric 3 it reduces the RAM usage (heap size) from 1,792 MB to 984 MB. For comparison the same setup with Hydrogen instead of FerriteCore uses 1,335 MB.
These values were measured after generating a world with a fixed seed and waiting for two minutes. You may notice that the setup is different from the Forge version, where I compared memory usage at the title screen. This is because Forge populates some caches (which are optimized by FC) before the title screen, while Fabric (and vanilla MC) wait until a world is loaded.
The project picture is a cropped version of this picture.
Should I install this on the server or just on the client?
Some optimizations are client-side only, but there are some rather high-impact optimizations that are relevant on the server too. So you should install it on both sides.
Is this compatible with [other mod]?
Most likely yes. The only known incompatibility was Hydrogen, which is fully compatible with FC 2.0.4 and above.