Ok. The anal glands are basically glands (two of them) that are located next to the rectal opening and they empty through a duct on each side right next to the rectum. They basically produce a very foul smelling liquid that serves marking purposes for territory and such. So from a functional need, they aren't needed for anything more than communication purposes with other dogs. To remove them is a very valid decision for those dogs that are having constant anal gland issues - blockages, infections, or need for expressions. I always say that this surgery is one that owners have to be aware of the very small chance of the complication of being incontinent after the surgery due to a nerve being injured during the surgery. For those owners that are ok with this small risk, the surgery can be one that eliminates a persistent problem. Those that don't want to risk this are then in a position of trying different diets to see if that can help. They can also learn how to express the anal glands to help keep their pet comfortable. Here is a great link on anal glands with diagrams.

http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=625