SPF is an email authentication mechanism published in the DNS records of a sending domain.
It shows a list (called SPF record) of authorized IPs that can use this domain to send emails. As this list is public, the receiving server will be able to compare it with the IP of the incoming email.
It allows:
SPF, just like DMARC and DKIM, is a security layer to ensure email safety.
As for any email security protocols, having an SPF properly set improves the deliverability of emails sent from this domain.