This really incredibly awful book I am reading (_When Gadgets Betray Us_) says that Edmunds advises you "never to leave registration or other personal information in the glove compartment". I have not been able to find a source on the Edmunds assertion (so don't believe it until you do), however I've found other police departments and other web sites who duplicate it. Some of them specifically advise you to carry the registration in your purse or wallet.
Years ago, I had a friend P. P. had an older Mustang (no, I don't recall the year. At the time, I knew a bunch of guys driving older mustangs and a lot of them were from the 1960s so possibly P.'s was too or maybe I just misremembered). P. had a car stereo. You know where this is going. So when P. replaced the stereo in the late 1980s/early 1990s, he got one of the ones where the face plate pops off. When he parked it when out for the evening, he'd take the face plat with him.
P. got a really nice leather jacket. He put this face plate in this really nice leather jacket and then, because he was used to wearing a really crappy denim jacket that not even a homeless person would steal, left it at the table when he was dancing. Needless to say, the jacket and the car stereo face plate were gone when he returned to the table. Not a good night for P. And no way to replace it.
That's probably the best example I could ever come up with for why I don't take things out of glove compartments and carry them around on my person. I'm not the kind of person to misplace my wallet or purse on a regular basis, but I'm not going to create that kind of hassle for myself, either. I would understand advice to not leave the title with the car (duh) but this advice seems really strange to me. The theory is that thieves could somehow use the registration to sell the car, which strikes me as wildly implausible.
Finally, and this is really the clincher for me, my husband and I carry keys for each other's vehicles, because we never really know which one we're going to be driving. If we had to remember to transfer paperwork back and forth, well, let's just say _that_ would never happen. This piece of advice seems to assume one-driver-per-vehicle, and thus strikes me as asinine and stupid. Even if we made copies (would that satisfy a police officer? I have no idea) so we each had copies for each vehicle, think about the implications of carrying _that much_ additional paperwork around in our wallets or my purse all the time.