The use of a segmented system reduces magnetic flux "eddy" currents, which are losses. Instead of having large eddy currents in a solid core, you have a bunch of much smaller ones, which apparently is better. Which is the same reason pwer transformers use many plates instead of a solid core.
This page explains it.
Using segmented system may also have something to do with reducing hysteresis, but not quite sure on that. It's been a LOONG time since I was in shcool studying magnetic theory.