I read this article awhile back, but haven't seen anything discussed here about why you shouldn't express the anal glands. Just throwing out an alternate viewpoint.
"How Injuries Can Occur to Your Pet's Anal Glands
Many injuries to an animal’s anal sacs are caused by well-meaning but misguided groomers, veterinarians, and pet owners.
Many groomers are in the habit of expressing the anal glands of every dog they groom, as a part of “included services,” along with cleaning ears and trimming nails. Routine expression of healthy anal glands is simply unnecessary, so if you take your pet to a groomer, make sure he or she isn’t performing this “service” on your dog, which will weaken well-functioning, self sufficient gland musculature over time.
Many veterinarians, unfortunately, immediately express an animal’s anal glands if the owner mentions the dog “scoots” occasionally. This approach doesn’t identify or resolve the cause of the problem, only the symptom.
And believe it or not, many dog guardians decide it’s in their pet’s best interest to express their anal sacs on a regular basis. Again, just as manually draining other glands in your pet’s body is unnecessary, expressing healthy anal glands can stir up problems. If a dog is having recurrent or chronic anal sac issues, it’s important to identify the root cause.
The anal sacs are delicate little organs that can be easily injured with unnecessary squeezing and pinching. Trauma to the glands causes inflammation, which in turn causes swelling. Swollen glands can obstruct the exit duct through which the fluid is expressed. If blocked secretions build up and thicken in the glands, it can lead to impaction.
Routine manual expression will reduce the ability of the anal glands to work on their own. The condition of the glands becomes compromised, and ultimately they become completely ineffective."