I had a friend in high school who was able to take untimed tests. I later heard a teacher griping, because they didn't think my friend needed them. (I agree.)

My friend had a very good life, until he took a job that really clashed with his, uhm, tendency to be a perfectionist. When we caught up (because we hadn't spoken in a few years,) it was clear he didn't have much insight into how his perfectionism worked against him in the job. (It was a job where quantity was more important than perfection.)

What would have helped my friend more? Not the diagnosis that he needed untimed tests. Instead, counseling where he understood his difference, how to make best use of it, and when he needed to let go and not be a perfectionist.