Corporations and many other businesses can use this type of letter as a precursor to a formal agreement. In it they can list the salient points of their intentions and what they intend to include in formal contractual agreement if both parties can come to an amicable agreement. Thus it can be used as a fall back document should any questions arise during the final contract negotiations. A good example of this might be a letter sent to a company's investor explaining their intentions to buyout another company and what it is expected to do to the value of their stocks.
Thus, a document (the letter of intent) that the parties had started out viewing as non_binding and unenforceable, had changed from being that, to being a final agreement! Pennzoil, on the other hand, ended up with บǒ billion (later settled for ū billion) from Texaco for interfering in its deal with Getty Oil.