Can a service business grow too big?

I had a customer today ask me if I planned to add additional writers to my staff. Now, I have a long term plan which includes office help for non-writing tasks, but another writer?

As a service business, when you are the person providing the result your customer is paying for - you come to a point where you either decide that you've grown as big as you can personally handle and that's okay with you.

OR

You decide to take on others and perhaps compromise the quality of the service you provide.

You know the saying, "If I want it done right I have to do it myself."

So what do you think? Does it compromise your brand if you add people to your company?

I know what Michael Gerber of E-Myth Revisited and E-myth Mastery would say.

What do you think?