[Altaco]

Meanwhile, you discover a long time down the road that the algorithm you thought was fine is actually incredibly slow when scaled to large inputs because you didn't have a good understanding of runtime analysis.

Or maybe, as you say, understanding more things makes you worse at coding. Who knows.

[waterlesscloud]

I guess I'm not buying that Big-O is a necessary requirement to understand how fast or slow an algorithm will be. It could be that someone understands and uses the process behind it without being at all familiar with the notation.