I was in the lending section and saw some posts locked. Why would someone lock threads? What purpose does it serve? When should I lock threads?
Since you mention the lending section, let's make a common scenario:
Someone needs a loan, posts a thread, a lender comes up, filles the loan, the time passes by, at the repayment date, the loan gets repaid and the lender confirms the repayment.
If there are no complications, both parties are now done with the "trade", hence nothing more has to be said/written.
It's time to lock the thread.
Also, that guy just made a good point for locking the thread. Not what he wrote, but the very existence of his post.
People lock threads because they don't need the thread anymore or just no one has replied in a very long time. No other reasons really.