The rates oft-quoted in a GFE are what they are at the moment - not what they are upon the signing of the loan papers. The GFE can be manipulated with little difficulty. "Oops, there was an extra fee there! Oh, did we forget to tell you about costs that we don't have to disclose on the GFE?" Ethical lenders will do everything they can to clearly explain the fee structure and interest rates, but as today's struggling market attests, not all lenders are ethical.
Likewise, since interest rates are swinging like a maladjusted metronome, lenders never know if they are going to get on the good side or the bad side of a real estate deal. That's another reason for passing on their projected losses onto their borrowers.
Finding a good mortgage is essential if you plan to purchase a home. It is essential to pay for the house. There are several great mortgages out there. However, you have to find the best fit for you. You also have to take time finding a good lender. You may think that you already have the best deal, only to find that there are so much better. You have to take time finding a good mortgage.
When you speak of good faith estimate, it is one of the most effective tools in comparing loans. This amount gives approximation of the total cost presented by any financial transaction and thus comprises a big part for evaluating a mortgage if it has favorable terms or not.