I went to the university half way through my undergrad to file for a disability because I have ADHD and I go through short periods where my medication just stops being effective for whatever reason.

It's not a major disability but it was a barrier to me performing at my best so I filed the paperwork and got some minor accommodations. It was basic stuff like letting teachers know during periods when I was struggling and they would allow me to take tests in a separate room (same time limit, just by my self in a quiet room) or allow me an extra 24 hours on certain assignments provided I requested it X amount of days ahead of time.

Certainly they provided a minor "advantage" but not substantially. And these were things that most teachers are already generally willing to accommodate regardless of disability but the disability system provides a formal framework for doing so and avoiding the justifying yourself over and over again (vs just getting it cleared up at the start of the semester).

Disabilities come in many shapes and sizes. Most of them are small and it's way easier to deal with an office that deals specially with disabilities to come up with accommodations that make sense for you and keep them consistent across your entire time at university than it does to try and negotiate terms with every single professor or TA.