The Eurovision Song Contest introduced semi-finals in 2004. Last year, I noticed you are only allowed to vote in one of the two semi-finals, the one your own country is in (unless you're the host, or one of the five permanent countries). What is the reason behind this?
I thought of one theoretically possible reason which is very unlikely: if you could vote in both semi-finals, and your country is in the first semi-final, you could vote for poor contestants in the second one, leading to less strong competition in the final (if your country qualifies, of course). But then, why would the five permanent countries and the host nation be allowed to vote at all? So that can't really be the reason.