The way regulatory authority works is that Congress writes laws that offer general guidance, and then regulatory body creates rules around that guidance. It can enable them to quickly react to changing scenarios, and also offer greater expertise or more detail than may be reasonable to expect of Congress. The issues arises when it's unclear if actions and guidance are aligned.

For a contemporary example, part of the CDC's power comes from Section 361 of the Public Health Services Act [1], which grants them the power to execute orders to prevent the spread of disease into the country or in between states. Examples included inspection, pest extermination, fumigation, and so on. The CDC invoked this power to prevent landlords from evicting delinquent tenants during the COVID stuff.

That was a gross enough (and also, critically, harmful enough) violation of their mandate that it was able to be challenged in the courts and eventually tossed even in the Chevon Deference era, but a lot of scenarios are much more ambiguous. So now their actions will be fully subject to oversight from all branches of government. The end result is that executive departments will have a much harder time overstepping the bounds of authority granted to them by Congress.

[1] - https://www.govinfo.gov/content/pkg/COMPS-8773/pdf/COMPS-877... (page 405)