Division 01 covers items such as allowances, alternates, submittals, substitutions, temporary facilities, cleaning and closeout. Each technical section refers back to it.
Example: a gym equipment section says to submit product data per Division 01. The Division 01 submittal section sets the number of copies and the review time.
Specialty bidders skip Division 01 because it is long and not about their product. Read at least the sections on alternates, allowances, substitutions, submittals and closeout. They change your price and your schedule, and they bind you through the subcontract.