Most industrial cameras have some way to adjust the video gain, so you can still film under inadequate light, albeit with a noisier picture. This camera differs in giving you two levels of AGC, rather than two levels of fixed gain. You have an AGC off option, with low or high AGC (apparently ≤+9 dB and ≤+18 dB).
Even with the AGC switched off, there still seems to be some sort auto-level control happening. If you adjust a manually controlled iris to the point of white clipping, you can see the whole video signal drop down the more you fill the screen with the white object. So you'd be hard pressed to do a shot with a person against a washed out white background, for example, and manage to keep the scene properly exposed.
Professionals cameramen will, generally, want fixed gain, because they want absolute control of their exposure (manual iris and gain). Amateur cameraman, and other people needing a camera for special recording purposes, may prefer more automatic controls, allowing them to get a picture out of the camera, even if less than perfect.
The camera also has an auto-iris control, which adjusts for some sort of average picture level, though it has reduced sensitivity along the very top of the frame, ostensibly so that bright sky (or bright lights) appearing in the top of the frame doesn't unduly cause the auto-iris control to close the iris down. Like many auto-iris controls, it's often set up to over-expose to some degree, though you do have a manual override to control the average level. But, by the time you get to fighting with the auto-iris to properly expose, it's far easier to do fully manual exposure.
The AGC is more of a peak level adjustment. Increasing the gain until a significant portion reaches a peak level. And, conversely, reducing the gain, a bit, during over-exposure.
Although AGC and auto-iris can potentially fight against each other, they do seem to co-operate well together in this camera, up to a point… If you have a medium contrast scene you'll get a reasonably good picture. But you'll notice differences between two cameras operating on automatic controls, and some inappropriate changes in video level as you adjust your shot around, or people move around in your shot. And the usual problems with auto-exposure cameras, when it comes to very contrasty scenes.