Regardless of being mandatory for accepting a "low bid", you can bet there will be "change orders" leading to "cost over runs". Contractors make note of any potential "change orders" to use as a wild card in hopes of recouping any losses from proposing a "low ball bid". Not a bad thing as good contractors need some leverage to compete against the shoddy contractors. Problem is, these "change orders" can be used to conveniently increase payment to 'Uncle Charlies Construction Firm' so he can substantially underbid all other contractors. Remember who approves any "change orders" that, can produce some hefty "cost overruns" and the general public will never know why a $150.000 roofing job cost $255.000.
Project managers, Inspectors, Clerk of The Works, etc. are people who represent the owner and are charged with overseeing the project. If these people are on the up and up, "change orders" are usually scrutinized line by line and may not be recommended, to the owner, as submitted by the contractor. However, if 'Uncle Charlie' provides for this 'representative' of the owner, well, chances are the dude shows up once in a while and, never reviews any "change orders" let alone, assures 'Uncle Charlie' is following the contract. Nor do the owners care!!!!
I hauled asphalt for a contractor for about 3 weeks and in that time we resurfaced miles and miles of secondary roads in PA. All contract work going, to the lowest bidder. The inspectors, college students of, parents employed by PennDot.
Their job, stand around with a thermometer and a clip board to record the temp. of the asphalt and, to watch for any diesel fuel that we might be using in the bed of our dump trailers. Meanwhile, the army of Penndot workers were busy cleaning ditches along with tarring and chipping roads that the contractors will likely be resurfacing with asphalt next year.
Why does Penndot bid this type of work....... because the contractor can resurface the roads, with asphalt, cheaper then a state run unionized workforce can!