Why did Jerome feel that his visit to a doctor would do a doctor a good turn?

Jerome thought his visit to the doctor would be a good turn because a doctor needs practice.... and give him all the "practice" a doctor could ask for.

I went to my medical man. He is an old chum of mine, and feels my pulse, and looks at my tongue, and talks about the weather, all for nothing, when I fancy I’m ill; so I thought I would do him a good turn by going to him now. “What a doctor wants,” I said, “is practice. He shall have me. He will get more practice out of me than out of seventeen hundred of your ordinary, commonplace patients, with only one or two diseases each.”