Hello, I understand the point you are trying to bring up.

There is no doubt that the real business does not happen when a customer decides to choose your company to do a project, the real business happens when that same customer comes back satisfied to your company in a satisfied way and asks you to do a second project because the first one was excellent. Missing a milestone causes the project manager to miss all the due dates previously established. I don’t think there will be a customer who gets satisfied when they find out that their project has been delayed. That is why you have to be as detailed as possible in the planning phase, so that when the executing phase arrives, there are less chances of making a mistake which will make the customer happy, which will make that customer come back and make more profit for the company.

Additionally, I agree with someone up there who mentioned that the consequences of missing a milestone totally depends on how important the milestone was. But I do not think that missing a milestone could bring some type of future success for the company.

Let me know what you think!
Sincerely,
Roberto Pineda.