You can do that, although I think you would have to pull first, merge locally and then push the changes in order to merge them. But you can also use actual branching, which is similar.
Advantage of 'real' branching is that you don't have to have two complete clones (in addition to some additional advantages depending on how you use it).
The disadvantage is that you have to toggle between branches if you want to switch working on them, so you cannot work on two branches on the same clone at the same time. Also, any uncommitted changes also shift to the other branch, unless they collide with changes made there, in which case you have to stash those changes. Anyway, a 'quick' toggle to a different branch isn't as easy as you'd hope.