You had probably read one of my posts on the subject. I've never had an acrylic large tank, but have heard the horror stories firsthand. Having owned big puffers and triggers, they are often in the habit, as others have stated, of biting at the display panels to get your attention or to nip off stray bits of microalgae, etc. Think about this happening every day for several years.
You can hear such activity from another room. If a trigger's or puffer's teeth can crunch up shells and pieces of coral rock, they certainly can scratch up acrylic. They won't take bite-sized pieces out of it, but they will scratch it. Thankfully, glass is harder than their teeth though.