Sources may use a handfull of names. So if you give "person x in country y" to someone, and they don't use it, if they are LE then it is fairly simple to get WU to cough up the pickup history for person x. I'm almost certain WU will not even bother to fight the RFI, why would they? Point is, LE now has info: where did person x do pickups. Should the source be less than bright, he may use person x's name again, and pinching him becomes a trivial exercise. If source is a bit brighter, that name is burnt, and source now has one less name for pickups, which he will need to replace. No matter how you slice it, it's a headache.