Understand the material
Before we can figure out why acrylic does what it does, we have to understand what acrylic is. Acrylic acid, also known as PMMA, is short for poly (methyl) -methacrylate, a plastic derived from refined petroleum and oxygen. It's not the same as polycarbonate, which is pretty hard to work with and is (at least for game mods) shoddy.
Acrylic acid is a material that is often compared to glass for obvious reasons. It is about half the density of glass (and therefore much lighter), and can convert about 98 percent of visible light through it. It will not pass through wavelengths smaller than 300nm, thus blocking harmful UV rays in the first place - but it can be treated to further prevent waves between 300 and 400nm (near UV). Due to its index of refraction, it can reflect off all surfaces (naturally about 4%), so some prism effects may occur. This reflection property can be adjusted by roughening the surface (similar to transparency).
Scratch more easily than glass, and break abnormally. Instead, when hit, it breaks into larger pieces by breaking apart. Although it is much more durable than glass, it can't withstand the intense pressure of the glass surface - so it can withstand some bumps and scrapes, but don't expect it to withstand sledgehammers. However, not all acrylics are created equal, so the type of acrylics you buy later has a lot to do with the durability of your acrylics.
Acrylic acid can be manufactured in two ways:
Extrusion, polymerization, melting (about 250 degrees Celsius), pouring into the die head and air cooling; Or,
Battery castings, simultaneously polymerized and molded in a mold.
The difference between the two products is like day and night - because of the way they are made, the strength is much weaker when pressed and it is prone to shattering or cracking. This is because as the material is pushed through the die head, the polymer chain stretches and orients itself in one direction. But since all it takes is a big furnace, a molding mold and some space, extruded acrylic is very cheap.
Battery casting, on the other hand, requires a mold made for each piece. These molds must withstand the chemical properties that form the polymer, and the final acrylic acid must remain in them until it cools. This means many molds and a slower end product, making the casting cost of the castings much higher. However, because the "lattice" of the polymer occurs naturally in its final shape, the lattice casting is more durable, scratch-resistant and crack/shatter resistant.
All in all, if you're going to cut or sculpt cells in any serious way, it's worth every penny. If all you need is a flat piece of stuff, squeezing might solve the problem in a pinch -- but don't say I didn't warn you!
Why use it?
Knowing what acrylic is, it is easy to see why we would use it as an ideal case building and decorative material. It's softer than metal, and the Anti-static Plastic Sheet is anti-static, so it's safer and easier to use. It is more difficult to break than glass and will not shatter if broken, so it will cause almost no damage when placed in place. And it's lighter than glass while still being transparent, which makes a big difference.
Better yet, due to its nature, it can be easily milled, cut and machined using ordinary woodworking tools, unlike glass or metal. True iridescent color, translucent and reflective make it easy to add to any mod. There's even pearlescent material!