I heard that once it's done repeatedly at the groomer's, they lose the muscle tone to express it themselves. I only express it when necessary or when the customer requests it, even after I tell them the above. Yes, it can get impacted if not expressed or expressed wrong & cause an abcess.
Mimi licks her bum when it's time to express. Since I've changed their food, she doesn't need them expressed as often. I hardly ever have to express Momo, only when he scoots.
Mercury, lift up Thor's tail, & feel around the 5 & 7 o'clock, if there's a bulge or fishy smell, he might need it expressed. The vet expresses them too, sometimes internally.
Anal Sacs
Priscilla, Princess has an outtie too lol...I don't think that matters.
I forgot to add that I also give them thawed diced up green beans mixed in their kibble. It has fiber, so it bulks & firms things up & it's supposed to help them naturally express when going #2.