I see two main benefits of using paper ballots. The first one is that is easy to explain and everyone understand how it works. Your grandparents, probably your kids of a certain age... When you start talking about electronic voting, the system becomes much more complex, and you need to trust someone else assessment of the system.
The second one is that you can enrol interested people in the process, for instance during the vote counting. In France, any voter can register to participate during the night. This creates a sort of community engagement which is extremely important in my opinion.