And if you DO have teenagers (especially ones that drive) and you think that they are telling you everything about where they are going and what they are doing, then you are incredibly naive. I'm sure you never lied to your parents about what you did growing up <snicker>.
I never did.
Am I unusual?
What are the reasons to using FMF to check the exact location of one's kids on a daily basis?
Same reasons I check on my wife:
1) I don't start dinner until I see she's on her way home without having to bother her at work with phone calls.
2) If I'm about to call and check in (as you say you'd also do) but I see she's at a friends house or the grocery store, there's no need to bother them.
Basically, you'd check on your kids but bother them with a phone call and I'd check without the phone call. The privacy implications are IDENTICAL between you and I, but your kids are gonna get bothered by a ringing phone a heck of a lot more often.