I had a bit more fun with my math degree than the author did, but the curriculum taught me similar things.

I'd add one more: I think it helped me be a better writer. All of college and the closing out of adolescent cognitive development probably contributed some of that too, but I noticed that by the time I'd made my way through analysis classes that I was getting better responses to my written communication and that I could detect a tightness in some of it that was familiar. I think it came from spending so much time trying to clearly articulate details of abstract concepts that I was struggling to come to grips with. A proof is arguably a (very specialized) form of a persuasive essay designed first to illuminate and convince oneself.

Perhaps it contributed to the author becoming a better writer too.