In Summary

Channel masks are the jewel in the crown of your selection tools. Sometimes they can make easy work of an impossible-looking selection. And when they work you feel like you've arrivedin Photoshop terms at least. Because every image is unique, there are no off-the-shelf, one-size-fits-all solutions. But after experimenting with channel masks you'll quickly develop an instinct for when they are the best way to tackle the job and for what other techniques, if any, you may need to use. Basically, if the subject of your image has fine edges, a dominant color, and reasonably good edge contrast, then a channel mask will work. If not, then perhaps a channel mask is still appropriate for part of the selection.