Normally, anal sacs empty with the pressure from a bowel movement. If stools are consistently soft or too small this action is thwarted. If this is your problem the addition of fiber into the animals diet can be remarkably effective. With domestication come problems and man made, overly processed diets are often substandard in this regard.
For most animals manual emptying of anal sacs causes them to produce more discharge, so the situation kind of feeds on itself- the more you empty them the more you have to empty them. It is my opinion (as a groomer of many decades) that we should not automatically express anal sacs unless there is a clear need to do so. I know- they smell. But that is their function, and I'd have to suspect that more production is keyed somehow to a bodies perceived need for more scent to mark with.
There is also the possibility that any secretion is a bodies attempt to rid itself of something. Processed food additives would be my guess, but I have never heard this theory properly discussed so who knows if it is a valid point or not.
Incorrect emptying also causes problems. The sacs become bruised and often the nature of the discharge changes or production itself is increased.
Why some animals develop infectons and/or abcesses repeatedly has not IMO been fully answered, but it is my opinion that it most often hinges on diet. Animals bodies should operate correctly in this regard without human intervention. Anything a body does it does for a reason be it a misguided one or not, so figuring out why it happens would be key. To my knowledge there has been precious little research in this area, so could be we will never know.
So do you express or not express?
If the cat has a real problem then I guess you have to. But I would certainly look at tweaking the diet a bit with increased fiber in hopes that the cat is able to handle it on its own. If that didn't work I'd have a discussion with my veterinarian and ask them these hard questions.