This part attaches a Raspberry Pi in a slightly stupid case I have to an external hard disk. There wasn't really a way to print it without at least some kind of support material...except leaning back at a 45 degree angle. This printed entirely without supports.
Glass is absolutely not guaranteed to be flat or without defect. Some glasses are. Mirrors have to be or they don't work, they come precut in 300x300mm plates for cheap from IKEA. You're free to check absolutely any thread from the time to see what people's motivations were. Moving mass on a bedslinger would've been a bigger consideration.