Under Chevron, a court defers to agency interpretations of ambiguous statutes, as long as the judge finds the interpretation to be reasonable. If the court limits or upends the Chevron doctrine (which the SCOTUS did), the ruling would pull back the leeway that agencies have had in interpreting statutes.
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For example, now the FCC no longer has the power over topics like Net Neutrality ... that is now left up to the courts.
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The historical stance on this was, agencies should have authority over ambiguous statutes because they are Subject Matter Experts in the space (you can't expect a judge to be a SME on every possible topic).