What would you look for in a coach or a mentor?

For simplicity, let's say that:

- the role of a coach is more strategic, working with you over a longer period of time to help you to achieve longer term goals - the role of a mentor is more tactical, offering advice or feedback on specific situations day-to-day

As an engineer:

- Have you ever considered working with either a coach or a mentor? - What kinds of things might you ask someone like this to help you with?