I'm being added onto a team plan. I can choose to cancel my individual plan or keep both. What is the real advantage of keeping both?
If both the individual & the team plan are registered to the same Adobe ID, then you should cancel one of them as you can activate CC only two times. The only advantage is of getting the storage space of 120GB.
It is perfectly fine to cancel the individual CC, to cancel, please refer to: http://helpx.adobe.com/x-productkb/policy-pricing/cancel-membership-subscription.html