How does it work?

Internally, the mod simply goes through each planet and space location on the settings list, then modifies the harmless and dangerous asteroid spawn rates, according to the user-defined multiplier for that planet/space location.

Compatibility with Safer Asteroids

Safer Asteroids runs after Asteroid Frequency Multiplier, so the changes to harmless and dangerous asteroid spawn rates will apply first, then (if necessary) the dangerous asteroid sizes will be modified.

For example, both harmless and dangerous asteroids can be increased on any planet by Asteroid Frequency Multiplier, then the dangerous asteroids can be rendered harmless by Safer Asteroids; as a result, both of the additional spawn rates would then apply to the harmless asteroid chunks.

If dangerous asteroid rates are reduced before being rendered harmless, without an equivalent increase to the harmless asteroid rates, then the planet will have fewer asteroids in general (when compared to vanilla).