Seems a strange question to ask a company whose (kinda) jokingly professed goal (at least by the CEO) is to make coaches obsolete. 
Here’s a few cents: when you are paying a coach, you need to understand his or her coaching philosophy. What are they providing you? If it’s just a training plan, you’re right, you can find plenty of those… but what is the basis of that training plan? WHY does that coach prescribe the workouts they do at the time that they do? TrainerRoad has a training philosophy. When you pay them for a subscription to follow a plan, you’re getting a plan structured a certain way. What you get from a coach will almost certainly be different.
What are the constraints of your training? Are you time and volume limited? Do you have more time to train than you can realistically use?
The use cases for a coach vs. TR vary widely based on those constraints.
Is it your intent to blindly trust a plan? Or do you want to know why that plan will work vs. a different plan based on your constraints?
Are you needing to train specifically above FTP? Do you need to raise your VO2max? If so, when? Are you limited by it, or do you have room to grow?
These are just examples of what a good, well-educated coach should be helping you with… and educating you about. They say nothing about nutrition, race and ride execution, equipment, psychology, etc. etc. I view an outsize part of my job as a coach to teach my athletes how to train (and why that way) such that someday, they don’t need me anymore, appropriate to their specific life circumstances.
At least that’s one coach’s philosophical take on it.
A coach is not just a training plan. If your coach is, yes, odds are good you’re wasting some money (IMO). I have said before and still believe that for many people, TR is among the best values out there in cycling training.