When importing a managed solution, use the upgrade option unless there is a specific reason not to
While a patch exists for a solution, the solution is locked and cannot be directly edited. Multiple patches can be created for a solution
Cloning a solution incorporates and deletes all the existing patches. A cloned solution is unlocked and so can be edited directly
Patching too frequently isn’t recommended because it increases complexity when storing your solution in a source control system
Here’s a great vid from Brian Knight of Pragmatic Works demonstrating the step-by-step process of patching and cloning