After going through a web dev bootcamp myself where we actually devoted a decent amount of time to algorithms and their time/space complexity -- this has been the thing I have used the least in my professional career.
When I work with large data sets, It's difficult to explain why something is taking a long time without thinking of it in terms of O complexity.
Sometime in my third year on the job I had to find the duplicates in an array. My beautiful solution "arr.select{|x| arr.count(x) > 1}.uniq" didn't work because I had 100,000 items in the array. My solution was O(n^2), and that finally made sense to me, and it actually mattered.
I would say this was when I didn't feel like a Bootcamp beginner anymore, and thought of myself as an intermediate professional programmer.
What do you mean by, "not working on professional things"? Seems a bit insulting to me?
If you don't know how to handle algorithmic complexity it's less likely you will take a job that demands knowing much about it, but that doesn't mean it's not professionally needed.