If you're just starting out and getting more serious about biking, a coach is invaluable. This is my first year training for any sport and there's a huge difference between doing something alone and doing it using the knowledge and tools of someone with 20+ years of experience who has coached guys who made it to high levels in their sport.

And you get to meet a lot of new people to train / ride with.
For me the social / networking aspect is worth it.

But it is expensive. If you have limited money, a power meter is probably the best possible training investment you can make. You're infinitely better off with a 1000$ bike and a power meter than a 3000$ bike and no power meter, and I think that you'd also be way better off with 2000$ worth of coaching over 2000$ worth of bike upgrades.