The advanced regulator helps fully automate a breeder because of the multiple specific output slots. For example, say you use the breeder with two isotope stars. You can set one regulator to output 8 depleted isotopes to 8 exact spots in the reactor defined by the number grid on the right of the UI, then use another for the uranium cells. This prevents issues with, say, an export bus filling the isotope slots with uranium and causing a meltdown, and also prevents the necessity of several machines all outputting to one slot each. It also makes it easier to automate you can just put a level emitter on the bus attached to the uranium advanced regulator and tell it to check for 170 isotope cells (around a full breeder cycles worth). My setup uses two adv regulators, one for uranium and one for isotopes, each with their own export bus, a level emitter on the uranium adv regulator, and an import bus on the reactor set to re-enriched cells. After I set it up, I never had to touch it again.
If you are running a small scale reactor setup, maybe automating the breeder isn't as easy and painless as just manually starting each reaction with two uranium cells and setting an export bus on depleted isotopes with an import bus on re-enriched cells. However, if you're burning through 500+ uranium cells a day, the automated breeder is critical.