Why is it important to evaluate capital budgeting projects on the basis of after-tax cash incremental flows? Why not use accounting data instead of cash flow? What is pay back period? Also, discuss...

Why is it important to evaluate capital budgeting projects on the basis of after-tax cash incremental flows? Why not use accounting data instead of cash flow? What is pay back period? Also, discuss the utility of the pay back period in determining the internal rate of return.