It has been debated alot. It is a pretty easy calculation to see if it is worth your time but you need to get accurate estimates from other lenders not just on the loan but on closing costs and that is super hard to do.

The biggest problem is the closing date. If the home you want to buy is not going to close escrow for 5 months or so then nobody can quote you a rate right now because nobody will give you a 5 month lock. Sometimes the preferred lenders give a long lock and they may have a 1 time relock if the rates go down. It is a tough call to make. Overall the lenders that are preferred by the builder are fairly competitive but do your homework and check other outsiders.