Eric: if you plan to stick with the in water DM who is totting the surface flag, you won't need to worry about using the SMB. Many people don't stick with the DM.... locals almost always shoot the SMB on a reel from depth when they are ready to come up and aren't with the DM. While I don't advise it, some divers (mostly tourists) will surface and then inflate their SMB if they are separated from the DM. Shooting from death allows other boats to know your coming up and gives your boat captain more time to locate you.
Is shooting a sausage from depth mandatory....probably not, though its a good skill to have when drift diving