Infrastructure management mostly — cron scheduling, DB migrations, nginx configs, log analysis. Things I know how to do but that are slow to type out. But the learning is there: I've used it to go deep on PostgreSQL query planning and indexing in a way I wouldn't have bothered with before.
The risk, in my opinion was the opposite of I'd expected — not learning less, but a lot of shallow things giving an impression of learning which in effect isnt there. Look! i built this powerful thing. 60.000 Lines of coded business logic in a week! On the surface i have something impressive to show. People admire it, and i end up believing that i did it. This is not to say that i did not learn - i did, but my learning was not as impressive as the result would make you believe.
Maybe i should try using it to learning Math now.