When Should You Use an Agent?

I’ve never actually rented my flat out myself.

When I went to work in Asia it seemed way too much hassle to try and manage my flat from 10,000km away. The first agent was a disaster but the second worked well for the next decade.

Was that a good time to use an agent? Was there a better way to do it? (Openrent didn’t exist then) and are there any other circumstances where it’s better to use an agent?

Or is openrent good for every circumstance?