Not all dogs will need to have their anal glands expressed. If their feces are firm, then when the dog defecates, the glands are squeezed as the poop passes by the glands and some of the liquid is excreted. This is the way it is supposed to happen naturally. The key to keeping healthy anal glands is to keep the feces firm....
Small dogs especially do sometimes have problem with blocked glands. One time I noticed that Edie was licking a lot back there, and then I noticed a big red bump above and to the right of her anus. I knew exactly what it was. It was anal gland that had become abcessed. We went right to the vet.
The vet put Edie under with gas and opened up the gland so it could drain. She was on antibiotics for 10 days. Oh--here is the good part---I had to put warm compresses on the area 4X a day to keep things draining.
But it really did not have much to drain and there was no mess or blood like the vet told me there might be. Fortunately, Edie never really seemed to be slowed down by the whole experience. She was her normal feisty self the entire time, which is one reason it took me so long to notice the problem.
The area healed up fine, and there has been no recurrence (it has been a couple of years). Edie eats dry food, and her feces stay very firm. I keep an eye out for her licking that area but so far so good.
So---I think the answer is, if things are working right, you don't need to have the glands expressed. Some dogs are prone to this and have recurring problems. If you have an older dog that has never had a problem, then you might NEVER have a problem.....Just be aware of it.