Leetcode's utility is not in showing you can solve real-world problems. It's used as a baseline to estimate how smart you are. Every shop prides itself on hiring smart people, and some only want the best of the best—your MIT and Stanford grads, etc. A smarter engineering workforce can not only solve the problems you have, they're better positioned to spot and avoid problems you haven't anticipated yet. Anyways, IQ testing as a condition of employment can open you up to legal liability, as IQ tests are horribly racist. Leetcode is a way around that.