Why raise a PO at all for a small trade business?
Because it is the only reliable way to know what you have committed to spend before the invoice lands. Without one, material cost appears a month later on a supplier statement and by then the job has been invoiced at the wrong margin.
Can I email the PO to the supplier?
Yes. POs are sent by email from Gaffer to the supplier address on the order, and the sent timestamp is recorded so you know when it went.
How do I know what has arrived?
Delivery notes are recorded against the purchase order, including whether everything was received and whether the condition was satisfactory, so part-deliveries and damage are captured rather than assumed.
Does this affect job profitability?
Yes. Because POs carry a job reference, ordered materials show against that job's costs, so margin is calculated on what the job actually consumed.