cies is correct but I'd like to expand the point. A junior engineer (like me) might have encountered tens of systems, and work in less than ten. Senior/more experienced engineers encounter and work in much more. They know which things to implement. For example, let's implement an authentication system for a SaaS. The junior engineer will ask for specs to the brim to avoid missing anything. How to do forget password? Password requirements? Social logins? While the experienced can see the contexts, pick the suitable decision and implement it quickly. They will be more concerned whether the auth will need to support OAuth to smooth out onboarding or to put it off later because their target demographic is more familiar with email/password. These kinds of shortcuts compound to reduce anxiety, increase velocity, and to iterate faster when the product hits the market.