This was a problem for me at first because I ended up with multiple accounts with no way to merge them together. But I believe they started with YouTube.
I got an email saying they will deactivate/delete the account without verifying it (in this case "verify" was to create a Google account). I'm guessing this was only sent to accounts that hadn't uploaded any videos and mine had none at the time. A friend of mine also got the same email and she had no videos at the time either.
It makes sense from their end to create one account, but adding Google+ seems to be a case of forced adoption. I've used multiple gmail addresses and they've all prompted me to create a new G+ account whenever I logged in just to check the inbox. If I wanted to add another service, I've been hit with some sort of conflict message. I think Google is able to tell when the same person uses multiple gmail addresses.