Quick Answer
Government buyers care about incurred cost submissions because on cost-reimbursement and time-and-materials contracts, the government pays a contractor's actual allowable costs, and the annual submission is how those costs get verified and settled. Commercial buyers rarely look inside a supplier's books, while a federal buyer paying actual costs must. The submission is due within six months of the contractor's fiscal year end, and being ready for it signals readiness for cost-type work.