Private versus public is not the important part here; interstate versus intrastate is. The US federal government was designed (via the commerce clause in the US Constitution) to be unable to regulate commerce that occurs entirely within a state, which should be entirely a matter for that state. Taken to its limit, that would mean, for instance, that federal laws about controlled substances would not apply to products produced, sold, and consumed entirely within one state, so there'd be no more ambiguity about whether the federal government can go after producers or consumers of marijuana in a state that has legalized it.

In Wickard v Filburn, the court effectively decided the federal government could regulate commerce occurring entirely within one state, on the theory that intrastate transactions could reduce interstate demand. That's an incredibly expansive and arbitrary justification, and effectively removed all limitations from the commerce clause. Invalidating that ruling would be a massive reduction in the power of the federal government to limit people's rights within a state, and an expansion of the power of individual states to make more things legal. (Note that individual states can already in general make things illegal that the federal government permits, so the primary effect of invalidating Wickard v Filburn would be to make more activities legal, rather than illegal.)

There would be a lot of fallout, and potentially a need for more targeted follow-up cases to confirm the legality of specific federal regulation that previously just relied on Wickard v Filburn; the outcome would not be 100% positive. But on balance it seems like a net positive.