This is what I believe is beneficial if you use Fibonacci:
1- You don't have to compare complexity relative to other stories that precise. If you are not using Fibonacci series, you may end up comparing which story is bigger twice or 4 times relative to another story, the idea is to have user stories with the lower points. So if you are getting to the higher point range, we don't want to have focus on them and decide if it is 4 times bigger than the user story assigned just now.
2- Fibonacci numbers can be found in many natural patterns, so it might be more natural to us estimating the user stories by them. https://en.wikipedia.org/wiki/Fibonacci_number
3- Back to the lower point stories, see the difference between 8 and 13 and 8 and 16. There is no in-between points. The whole point is to give flexibility when it comes to the stories you want to accomplish within an sprint (which should be fairly simple, so sticking to 2 3 5 8 13 would be way better than 2 4 8 16 32)
- (BTW the Fibonacci sequence has a 21 instead of 20, usually they simplify that and make it 20)
- (If I have to argue only by one, I would chose the 3rd one)