Speaking about whether it's really necessary to call Dispose on
CancellationTokenSource... I had a memory leak in my project and it turned out that
CancellationTokenSource was the problem.
My project has a service, that is constantly reading database and fires off different tasks, and I was passing linked cancellation tokens to my workers, so even after they had finished processing data, cancellation tokens weren't disposed, which caused a memory leak.
MSDN Cancellation in Managed Threads states it clearly:
Notice that you must call
Disposeon the linked token source when you are done with it. For a more complete example, see How to: Listen for Multiple Cancellation Requests.
ContinueWith in my implementation.