What does Section 2 of the 21st Amendment to the US Constitution do?

Question

Section 2 of Amendment 21 to the US Constitution says the following:

The transportation or importation into any State, Territory, or possession of the United States for delivery or use therein of intoxicating liquors, in violation of the laws thereof, is hereby prohibited.

What exactly is accomplished by this? Isn't something done in "any State, Territory, or possession of the United States" "in violation of the laws thereof" already "prohibited," because it is done "in violation of the laws thereof"?

If this is intended to clarify that states and territories can still forbid alcohol after the repeal of Federal Prohibition (a clarification which seems unnecessary anyway; why wouldn't they be able to?), why doesn't it say something like "The States and Territories shall have the power to forbid the transportation or importation of intoxicating liquors"?

Answer 1

State laws that impair the ability of businesses to operate on an interstate basis can be held unconstitutional and invalidated pursuant to a U.S. Constitutional law doctrine known as the dormant commerce clause. As Wikipedia explains at the link:

The Dormant Commerce Clause is used to prohibit state legislation that discriminates against, or unduly burdens, interstate or international commerce. Courts first determine whether a state regulation discriminates on its face against interstate commerce or whether it has the purpose or effect of discriminating against interstate commerce. If the statute is discriminatory, the state has the burden to justify both the local benefits flowing from the statute and to show the state has no other means of advancing the legitimate local purpose.

Section 2 of the Twenty-First Amendment to the U.S. Constitution, prevents the federal courts from striking down state regulation of alcohol on dormant commerce clause grounds.

It also removes from the legislative authority of Congress the ability to enact legislation pre-empting state alcohol regulation or forbidding the District of Columbia, Puerto Rico, the U.S. Virgin Islands, Guam, or other self-governing territories of the United States from regulating alcohol. Indeed, this is the only authority that the United States government is denied with respect to self-governing territories of the United States.

While this issue doesn't come up a lot, it has been invoked now and then to uphold state laws governing mail order sales of alcohol to residents of those states, and other kinds of alcohol regulations that might otherwise be unconstitutional, in the face of various kinds of legal challenges to their validity.