I have heard people say:
"If you will excuse me please, I will leave you for a moment and visit the restroom."
and from the Collins Cobuild Dictionary:
"I wonder if you would be kind enough to reach for my umbrella"
"If you will just sign here, we will arange the money transfer this minute"
which stands in contradiction to what I was taught at school about conditionals. Does politeness justify this kind of sentence? What kind of situation is it used in?
They can be used to be polite, when trying to negotiate. They balance the tenses in the two halves to suggest equality of concession.