How does influence handicapping work?

[Russian Orthodox Revolution]

Is the +10 an advantage or a disadvantage?

[Benkyo]

You are bidding for your preferred side. You should always bid for USSR. If you bid 2, that means you are willing to give your opponent 2 influence to play as USSR, so if you do, the US gets to put 2 influence at start into any country the US has influence. If you bid 0, it means you don't care and will probably end up as US with whatever handicap your opponent offered to play as USSR. If you bid for US, you will get US with no handicap (because your opponent bid for USSR).

If you are talking about AI/fixed handicap games, +X is the amount of extra influence the selected side starts with. Typically +2 US.