For Maple and similar hardwoods (oak, ash, beech, chestnut, walnut etc...etc...) you will find that there is very little sap wood vs heart wood. And what little sap wood there is (example walnut) its still good and hard enough to keep in the board for whatever reason.
As a woodworker myself, and I mill alot of my own wood via Alaskan Saw mill or repurposed wood, sapwood is not discarded or removed. I attempt to use all portions of the wood as I can, depending the project. And even then, I have a tendency to keep my scrap to reuse in another project, or a jig, or in my lathe or if all else fails I use it in my smoker or as firewood for winter.
But, if you are looking for a good book explaining different types of wood and their uses, look for "The Essential Wood Book: the woodworker's Guide to choosing and using lumber" edited by Tim Snyder.
Good luck, hope that helps!
Kj