But it may well not be my spending habit. It could be work paying for the flights.
What about credit cards, store loyalty cards (which link back to your FF account), duty free points, where your likely to travel too (regardless of who pays)... This is all little snippets of information which by itself doesn't mean much, but put it together and it helps people build a profile on you.
I'm not trying to sound alarmist, it's just I also know what a a little bit of information can do in the wrong hands, and I also know that most people undervalue their personal information (such as their full date of birth).
Years ago when CC's still used carbons as a matter of course, people used to rummage through dumpsters to find carbon papers with CC detail imprints, this is the sort of level that some people will go to, all that's happening is these people are moving online and using snippets of information to do damage (personal gain for themselves).
Also the comment was made that a points booking wouldn't do someone any good, as it would be in your name, not the other persons name. Seriously, especially when using OLCI, when was the last dom flight you took where you had to show ID?