1. It's cheaper to do it later yourself or by some professionals (e.g. HomeDpot). The builders price is among the highests.
2. The sub floor and joist may need further tightening, screwing to cut the squeaks after you move in (typically after a period of time, say, 1 year). You may ask the builder to come back to your house after 1 year to fasten some areas with screws. If you already have your hardwood floor in place, it's not possible for them to work anything further. With carpet it is easier to them to work on because they can move it up and restore it with no diffculties.
2. The sub floor and joist may need further tightening, screwing to cut the squeaks after you move in (typically after a period of time, say, 1 year). You may ask the builder to come back to your house after 1 year to fasten some areas with screws. If you already have your hardwood floor in place, it's not possible for them to work anything further. With carpet it is easier to them to work on because they can move it up and restore it with no diffculties.