Belt sanders are not considered to be "instruments of fine woodworking" ... but maybe this is a mistake. There are plenty of times that an aggressive tool is required to make light work of otherwise tedious jobs. I discovered the real trick to using any tool, particularly a belt sander is to KNOW THE TOOL. When you realize this, you begin to understand it's capabilities, limits and drawbacks.
What I discovered is that a heavy grit on a belt sander is probably best avoided, unless you are actually planning to dig the garden with it or fell trees. 40, 60 and sometimes even 80 grit sanding belts will make mincemeat of wood very quickly. The can also leave scratches and heavy gouges in the wood that are very difficult to remove. Lesson #1 - when using a belt sander, start off with a finer grade belt that what you think you will need. If you do this you will get a much better "feel" for what the sander and the type of grit will do for you. If you are removing a finish, this rule is particularly useful.
One lesson I learned a while ago is that "plaster-of-paris" works great for filling in holes in gyproc, which is what happened when the piece I started to sand a piece of wood and all of a sudden it took flight and embedded itself in the wall of my workshop. Lesson #2 work safe, fasten your work down securely.
I also discovered that for some reason, when you try to sand across the grain, it is almost impossible to remove those scratches without actually planing off the top layer of wood. Lesson #3 - don't sand across the grain of the wood.
I also found that if you do not pay close attention to what you are sanding, even if you start off with a 2 x 4 plank, you will soon end up with a popsicle stick. Lesson #4 - Mark your surface with the wavy line of a pencil to monitor how deep you are sanding.
There are also some unique anomolies you may find with some woods and sanding grits. For example an 80 grit sand paper belt, for some strange reason, appears to take off as much or more material than a 60 grit belt when working with large leaf maple. I suspect the reason for this is the grain structure of the wood. This means you can actually take off as much material with a 80 grit belt and not worry about gouging the living daylights our of your wood.
Having used my belt sander extensively to refinish some hardwood floors, I can say I am quite comfortable in their use now, but this came by way of lots careful use and getting a feel for the tool.
Copyright Colin Knecht