[Swordmaker]

But say for a job requiring $200k + in materials our bankers will NOT loan us the money for the materials unless we file a lien at the start of the job.

That lien is the assignable collateral for the bank to lend you that money. . . It gives them assurance they can go after someone with greater assets than you (not that they won't go after you, as well) if you default to recover the principal of the loan.

[Bubba Gump Shrimp]

yup