when is it alright to borrow from a 401b plan?

Only if you are facing foreclosure, bankruptcy (and want to avoid), etc.

Consequenses? Lose your job, and you have 60 days to repay in full.

Otherwise about 40% in taxes and a penalty.

People that borrow struggle to pay back. Many can't.

401B plans are no longer in existence.

I believe you mean a 401K or a 403B plan.

If you are still employed with the company that holds the money, you can borrow the money. But while you have a loan out you can't contribute to the benefit, nor can you receive company money. Additionally, if you leave employment for any reason you have 60 days to pay the money or you owe a penalty and taxes.

If you are no longer employed with the company, you can't take a loan. You can withdraw the money and pay the penalty and taxes.

There are few situations when it is "ok" to withdraw the money or take a loan. This money is for retirement, borrowing now will just reduce your income later. You should not put money into a retirement plan that you need before age 59.

You need to check with your employer's plan administrator. Not all plans allow you to borrow. Some have strict requirements.

Also, you don't pay penalty or income tax on a loan. You are hit with the penalty and income taxes if you take a distribution.

It is bad idea to borrow from your retirement plan because you lose out on the higher return on investment. It may sound like a good idea paying yourself interest, but that small interest rate is much less than you would earn if you didn't take the loan.