Verbal conversations don’t leave a paper trail for evidence of the topic of discussion or agreement.
I have often found that a verbal conversation (by phone or in person) will get a quicker result than communicating by email. However that conversation does not produce any evidence of what has been agreed (unless it in minuted such as in a formal meeting).
The result is that although you have agreed on something (a deliverable, a price, and due date etc.) you cannot easily hold that person or company to that agreement.
After a call or direct conversation with a client or other stakeholder (such as manager, team member, etc), type any agreements (dates, scheduled meeting times, requests etc) into an email and send it to the client to confirm the details. This is particularly important when chasing payment or discussing variations.
By sending the email, you have a written record of the agreement. It gives the other party the opportunity to respond with agreement or clarification on the agreement. Or if they do not respond you still have that record stating the content of the conversation that is now date stamped and on both your and the recipients email systems.
A written record of an agreement is very important, and when that record is shared with both parties it is much easier to hold people accountable.