They give you extra xp when you use them daily on Battlelog. The next game you play, you're awarded a number of "Nation Ribbons" based on the tokens you redeemed.
They also help to increase your chosen nation's standing in the weekly listing on the site. I'm not sure whether there will be any significance to it in the future beyond just bragging rights, but who knows? I do find it strange that countries such as Trinidad and Tobago, Botswana, Papua New Guinea, and Djibouti are so high up on the list so far, though.
A nation's score is the total tokens spent on that nation, divided by the number of people playing for that nation.
I don't think I need to explain why it makes the leaderboard so strange looking.
Ah, I didn't notice that. So each nation's score is basically the average of all the players' tokens for that nation. I still don't see how all those obscure countries have so many points, though. It's gotta be either people messing around and picking Nauru or Azerbaijan for fun, or possibly armed forces stationed there with an Xbox. Although, most likely, it was just battlelog testing...
As to why the most points aren't on top, it seems to be ranked by season, this one being the beta season, which is apparently season 6. There must be other countries besides the current top 5 playing the beta, though, so maybe just more bugs? Who knows? I'm sure there will be a better explanation of the whole system, eventually.