The problem with that (pre everyone with a GPS) was that the CG and Navy plot in true (still do). If you give them a bearing in magnetic, they will not have your exact location if they had to come looking for you. They have no way of knowing, also, how much deviation is throwing off your compass.
Without a GPS (when, perhaps, your boat gets hit by lightning?), it would be in your best interest to learn how to do the calculation and to take a manual fix so that you can give them and you a better chance.
Excellent point. If you are in distress and don't have a "true" fix or DR estimated position, it may be better not to guess but rather give them your last fix/DR and let them figure set and drift from there. They are better at it than we are, much more experienced. And it's most likely that the first responder will be a merchant ship once the Coast Guard calls for position reports from any ships in the area. Most ships are in AMVER, which is a program where they agree to report their positions and respond if at all possible.
Also, if you're WAY out there and no electronics (you may have a problem but..) you have a portable radio (but no portable GPS which unlikely but humor me, maybe it's broken or soaked too?) and a ship is within sight and VHF range? Call 'em on 16, switch to another channel, and ask the Mate to give you his (her? yup, nowadays) position, which will be from GPS and their course/heading from gyrocompass will be True.
This is how the old-time trekkers would "bum a fix" after days of cloudy weather and no celestial fixes possible. So yeah, the farther offshore you get, the more most everyone is "True" ;-)
Sorry if I'm wandering off topic a little, but it's interesting.