Assuming the role of the paymaster gives you the role as the general contractor not a homeowner or client.  Contractors like to request down payments, contractors like to be paid in thirds, and contractors like to get paid in cash, All three things are a negative in the world of construction.
Contractors like to mark up material because they lay out money to buy shelf items or they make a phone call to vendor to place an order. These mark-ups add anywhere from 5-20% on material, multiply that by 5-10 items ordered can add hundreds or thousands onto your project's budget for no reason at all except to make the contractor more money at your expense.
All items should have a receipt, all labor should have a dollar figure, all subcontractors have a written estimate which will be filed and reviewed as the project matures. If changes are going to be made the dollar value for the change is already established disabling the contractor's ability to overcharge or withdraw money from you like many helpless homeowners before you
Another reason being the paymaster is important is that your relationship with the contractor doesn't get muddy.  The contractor will have 10% held back from the overall budget until all inspection comments are addressed, all punch list work completed and all warranty paperwork filed and handed over to the client in a neat binder.
The stress of money is removed from your project making it easier for you to manage your ideas and not have to deal with obstacles of business .