Purchase Requisition or Indent as its commonly called is a first available documentation of the requirement by User.
Its important for the following reasons:
a) Item/ Description can be clearly specified in the PR
b) Approvals can be modeled to ensure, not just every email turns into a PO and a prospective liability for the organization. Some degree of validation recorded in system will be available.
c) In event that budgeting is being implemented, commitment of purchase can be reserved much in advance giving spend visibility better.
d) The buyer will have better visibility and easy management of the work load associated with processing of Purchase Order.
e) At the time of receiving, the receiving clerk can reach out to end user to confirm receipt of goods for inspection/ delivery comments.
PR is not just a document, its and important step in the P2P process, outcome of which can be a sourcing negotiation or a Purchase Order. I guess, enough reasons are stated