"Is there something I'm missing? Aren't lift bags generally for recovery, etc.? I'm a rec diver...the only thing I'm recovering is me."
Points are: 1. rec divers sometimes need to do recovery (for example, weightbelts). 2. light salvage is a different task than sending line to the surface using a reel of some type.
Most comments in response to your post focused on use of lift bags or surface marker buoys to send up a line for use during decompression and/or for surface signalling.
For these purposes there are many opinions as to whether closed circuit or open circuit bags are preferable. An argument can be made either way.
Should you ever want to use a lift bag for light salvage, however, as Dee mentioned previously, IMHO this can be a very different task than sending line to the surface. Even if it's simply recovering a 30 lb weightbelt or a small outboard motor, it takes some practice. Some nasty things have happened when divers tried to bring up a dropped weightbelt without a lift bag. As you concluded, some practice time will be invaluable.
Also, if you need a SMB to be closed circuit, then an LP inflator hose is necessary. Whether you want to disconnect a hose to inflate the bag is something to consider. Under perfect conditions it is rarely difficult. Under less than perfect conditions it can be more problematic. Open circuit bags can be shot by simply exhaling into them, thus eliminating either disconnecting a hose or removing the regulator from your mouth to inflate the bag. Other options occasionally require either more steps, or more hands than are sometimes available. Some divers carry both.
For light salvage you might find that open circuit bags are preferable. Depending on how large and heavy the object is that you are recovering (and how sunk into the sediment it may be), the salvage lift bag should be inflated with a hose and inflator designed for this purpose. The objective is to break any suction, get the object neutral, and maintain it neutral as you slowly ascend. Like most things, its easier said than done. As most have already noted, time spent rigging and doing practice lifts will be time well spent.
For more information see this site:
http://www.carterbag.com/home.html
Other sites on salvage of heavier objects are also interesting, but not generally applicable to rec divers.
My .02, FWIW.
Doc