On the other hand, in case you have a LAN account, you might end up with a bunch of LAN kms, if it's an award flight on LAN metal that you book.
I booked a flight using BA Avios, but at check-in changed my FFP number to my LANPASS number, and to my surprise, I earned a boatload of kms, plus LAN segment credit, from that award flight!
Apparently their systems get confused when you book an award with another program's points but then change your FFP (say, at check-in) to LAN.
The actual reason I had changed my FFP number to LAN was simply in the hopes that the return two weeks later would show up for check-in at lan.com without having to manually enter the 6-character reservation code, just by being logged into lan.com. And, yes, that does seem to have worked, as now that reservation is showing up under my upcoming trips when logged in at lan.com, whereas it wasn't until I changed the FFP number. (I already had an intra-country round trip "within" the timeline of my longhaul round trip that I had booked through LAN, and I thought it be convenient to see both trips in the same place.)