Something I've never quite understood is the concept of revenue sharing on codeshares. I get the concept, not sure I understand the specifics.

For example, let's look at the YYZ-FRA route. Both LH and AC operate on this route, but setting aside price, upgradeability, etc., from a pure revenue, non-status passenger, wouldn't you rather fly LH? Anyone done both?

So I have to think YYZ-FRA is profitable enough for AC to continue to run it, rather than just letting LH take the route and revenue share it. I know LH and AC already code share their existing YYZ-FRA routes. Or is this just common in airline alliances - two airlines run their own metal on popular routes and codeshare the others for convenience?

Anyone have any wisdom?