Marginal costing is a technique that differentiates between fixed and variable costs. It involves charging only variable costs to cost units and treating fixed costs as period costs. This allows marginal costing to provide useful information for management decision making like cost control, profit planning, and performance evaluation. Some key advantages of marginal costing include simplicity, improved cost control by avoiding arbitrary allocation of fixed costs, and better analysis of alternative production/sales policies. However, marginal costing also has limitations like difficulty separating fixed and variable costs precisely and not representing profits fully by excluding fixed costs from inventory valuation.