They clear the lien and you keep them from being named a co defendant in costly litigation and possibly losing the revenue from whatever loan you "partner" has taken out.

If there is a property with several years of open back taxes, with a few years forfeited (offered at sale but not purchased), do they need to be paid off before closing?

No,  the deposit is forfeited for breaking the lease. 

You can raise rent or deposit to offset the risk of winter moveout, such as a new deposit she forfeits if she moves out in certain months.

We finally agreed that he would write up an addendum for the contract stating that if the closing does not take place by Wednesday 7/19, then the buyer forfeits the EMD and a release of contract must be issued right away.

The usual thrills and chills, but there was this one memory I still laugh about that happened during the inspection...A lady with too many cats to even know how many she had was foreclosed on (forfeited) by a private seller carry.

BTW, there exist some common law (judges rulings) cases where it is stated that the redemption rights cannot be purchased, forfeited or assigned in PA.Time for you to research the actual PA statutes and rulings - some of your book info isn't as accurate as you might want.

Failure to complete the transaction after the grace period can result in you forfeiting your escrow deposit.

You end up forfeiting it and it is returned to the original owner.

If the assets were obtained by ill gotten gains property may be forfeited and auctioned eventually.