As a Startup for both technical and business teams.
Great with one guy I worked with - he's not a full-time coach, but coached me when we were doing a raise. We ended up raising $5m, rather than $1m in a seed round.
He helped me professionalize the firm's pitch, my positioning, and more importantly, made me feel empowered.
I had a coach when I was in a corporate role, but he just seemed to spout business-speak, rather than help me grow.
The best coaching experiences I've had are TIME-BOUND and run like projects with regular milestones. Like Bill stated, a lot of 'coaches' will run you around on their knowledge.
Whether you're providing or looking for services, interrogate the structure of the engagement, not just the outcome.
It really depends on the expectations you have set for what you hope to achieve working with a coach, and then the kind of relationship that you establish by agreement. There are a lot of coaches out there who are more of a personal support system, not as many that are good advisors. What's most important is finding someone whose style works for you. It doesn't have to be your style, but it does have to move you in the way you need to be motivated.
You may decide a professional peer group serves you better than an individual coach. It's hard to say until you try. Look for someone with whom you at least share some common philosophy, and who has worked in your industry.