Years ago, I used Plaxo. However the geniuses behind that didn't think I might have more than 1 email address, more than 1 set of followers, so I would get suggestions from them to follow people I was already following.
In the world there are very few 1:1 correspondences that are timeless. So any time a system assumes that there is a pair of things that are in absolute 1:1 correspondence, I am mightily suspicious.
There are 2 interesting cases to ponder:
1:1 at a time and 1:1 over time.
1:1 at a time, I get. However there have to be rules/policies/processes or whatever to change to a new one. But even those are suspicious because we may have to account for the zero case. And it usually isn't bilaterally 1:1.
1:1 over time is much harder. If it isn't possible for two things to exist independently of each other (for each one there is always exactly one of the other), then we have to question why they are not combined. By the way there are often good technical reasons, but maybe not so many good business or policy reasons.
So a word to the wise, when someone tells you there is a 1:1 correspondence, then they may be talki8ng about a single world view and that you should at least explore the alternatives lest you be trapped in an expensive rethinking process.