Some effects will be relatively small. For example the SEC has authority to haul you into court, in a proceeding which reflects how the system is supposed to work, with the executive branch prosecuting the law and the judicial branch deciding it.
But the principle invoked in this case, non-delegation doctrine, is far reaching. The non-delegation doctrine is a theory, some might say a legal fiction, that says that Congress can’t delegate its power to make the laws, but can make a broad law and allow agencies can fill in details so long as Congress gives the agencies “an intelligible principle” for doing so.
This is not without basis—there is no obvious line to be drawn between Congress’s power to make laws, and the executive branch’s power to enforce them in a discretionary manner. There is nothing wrong with Congress making a broad law “fraud shall be illegal” and the SEC making rules for itself about how to enforce that. But clearly at some point executive regulation looks more like law making and less like an agency imposing guidelines for the exercise of its own discretion.
Historically the Supreme Court has been unwilling to police that line, but that could change. One thing I think you might see is greater scrutiny of agencies applying existing authority to enter new areas of regulation. The theory might be, for example, that it’s fine for the EPA to cut sulfur particulate targets, which clearly falls under the scope of the Clean Air Act, but that the agency needs new Congressional authority to do something like impose limitations on CO2 emissions, which involves a different problem than the Clean Air Act was intended to solve. There is already precedent in this direction, under something called the Major Questions Doctrine: https://crsreports.congress.gov/product/pdf/IF/IF12077
If you want to hear how this legal conflict directly plays out in a real case, the SCOTUS oral arguments for the recently heard West Virgina v. EPA are available via the Oyez podcast:
The most practical effect from my perspective (engineer that has to deal with regulatory permitting and compliance) is that it will hopefully act as an incentive for agencies to better cooperate with applicants, to do so in a timely manner, and to prevent permitting demands from going beyond what's explicitly required by statute.
Even where it's currently clear that administrative agencies don't have authority to deny a given permit application, they often have the ability to delay it indefinitely, or demand superfluous reqs[0] be met before approval. (Since current caselaw requires a 'final administrative decision' before being able to appeal to an Article III court, an indefinite delay is essentially a loophole for agencies to wrongly "deny" a permit while avoiding judicial review.)
Agencies will want to avoid court cases setting precedent that might broadly affect internal administrative regs/policy beyond the case at hand, and therfore the future overall autonomy of the agency. (Notwithstanding the current lawfare abuse of agencies entering consent decrees premised on feigned controversy.)
Court rulings would also better bind agencies to previous decisions, and better prevent permit revocation for arbitrary or political purposes (see Keystone XL revocation).
[0] For example, permits for natural gas pipeline compressor stations are currently only being approved if they are powered by electric motors, instead of (the traditional method) of NG turbines ("self powered" by siphoning a portion of the fuel being pumped). Even if you presume CO2 emissions fall under current EPA clean air act authority (they don't), the requirement doesn't actually reduce net CO2 emissions with respect to the project's environmental impact, since it just means a small amount of NG is consumed at a different point source, instead of further downstream.
Not only does this not reduce the overall NG consumption (and therefore not affect net CO2 produced), but it adds embedded and operating inefficiencies, as well unnecessary points of failure. (see: Texas deep freeze blackouts where some NG "backup" infrastructure failed because it required grid power to operate. Especially true in remote areas lacking any electrical infra like offshore/aggregating compressor stations.)
Here, the EPA uses permitting power to implement supralegal political policy beyond the statutory requirements, by stretching policy logic far beyond what would survive the most basic judicial review. Under the status quo, judicial review is almost always an additional cost to the applicant beyond the expensive initial permit application.
Judicial relief (or the threat thereof) that potentially pre-empts some of those bureaucratic costs would be a real game changer for both private projects and public infrastructure, in terms of both roi and time/effort to implement.
But the principle invoked in this case, non-delegation doctrine, is far reaching. The non-delegation doctrine is a theory, some might say a legal fiction, that says that Congress can’t delegate its power to make the laws, but can make a broad law and allow agencies can fill in details so long as Congress gives the agencies “an intelligible principle” for doing so.
This is not without basis—there is no obvious line to be drawn between Congress’s power to make laws, and the executive branch’s power to enforce them in a discretionary manner. There is nothing wrong with Congress making a broad law “fraud shall be illegal” and the SEC making rules for itself about how to enforce that. But clearly at some point executive regulation looks more like law making and less like an agency imposing guidelines for the exercise of its own discretion.
Historically the Supreme Court has been unwilling to police that line, but that could change. One thing I think you might see is greater scrutiny of agencies applying existing authority to enter new areas of regulation. The theory might be, for example, that it’s fine for the EPA to cut sulfur particulate targets, which clearly falls under the scope of the Clean Air Act, but that the agency needs new Congressional authority to do something like impose limitations on CO2 emissions, which involves a different problem than the Clean Air Act was intended to solve. There is already precedent in this direction, under something called the Major Questions Doctrine: https://crsreports.congress.gov/product/pdf/IF/IF12077