How broad is the command to not be “unequally yoked”?

Question from a reader:

The ”unequally yoked” passage (2 Corinthians 6:14) is usually applied to marriage. What about business associations? How far does it go?

Further, what about Ephesians 5:7 which says: “Therefore do not be partners with them”? It is referring to: “Nor should there be obscenity, foolish talk or coarse joking, which are out of place, but rather thanksgiving. For of this you can be sure: No immoral, impure or greedy person—such a man is an idolater—has any inheritance in the kingdom of Christ and of God”?

And how does all this square with ...