While the Sorcerer's Hat has become the icon for Hollywood Studios (for better or worse), there are other "lesser icons" that many associate with Hollywood Studios. You have the Earful Tower, the Great Movie Ride and there's also the Animation Arch. While today the Arch that leads into the Animation Courtyard is more of a symbolic symbol than anything, it used to have a far greater significance that is why it's in existence.
The purpose of the Animation Arch goes back to the early days of the Disney-MGM Studios. When the Disney-MGM Studios first opened, guests entered the park through Hollywood Boulevard and this area of the park was supposed to be Hollywood in its' golden era. As you walked through Hollywood, you reached the Animation Arch, which served as the gateway between the Hollywood part of the park and the Backlot area of the park where film production was highlighted. Back then, going through the Arch was the only way to access the Backlot area since much of the park area we enjoy today was closed off to park guests because they were working backlots and soundstages.
Now that we've established the function of the arch, let's examine why an arch. I mean, it could have been any sort of different gateway, right? The arch was chosen because it's an homage to the Hollywood production lots that had archways as well such as Paramount and Universal Studios. In fact, it's not a coincidence that an arch was chosen since Michael Eisner was CEO of Disney during the creation of the Studios and he had come to Disney after many years working at Paramount, which has a rather famous archway leading to it's lot.
Some changes have since come to the Disney-MGM Studios archway. First, to cope with the ever increasing crowds at the Studios, more and more of the Backlot area of the park was opened to park guests, and that in turn created new entrances to the Backlot area (Mickey Avenue, Commissary Lane) and the significance of the arch was diminished. Of course, in 2008 the arch received a makeover of sorts when the Disney-MGM Studios became Disney's Hollywood Studios and the logo at the top was changed to match the new park logo.
If you also pay close attention, you'll notice some more details besides the logo. Along side the main part of the arch are two smaller archways that are adorned with some intricate designs that celebrate the many facets of film and television production. You'll find tributes to the many forms of entertainment in films such as comedy, the Western or the gangster film. In addition, there's a display of the Carthay Circle Theater and the Chinese Theater as well as depictions of movie scenes being filmed. Many guests overlook these fine details but it's all part of establishing what this arch is leading you towards.