I find spending a few days writing a detailed, in-depth design document for a given implementation often saves weeks or more of development. In the immediate term it takes longer. In the medium to longer term a thorough design can often lead to fewer bugs, less severe bugs, and less complicated enhancement development.
What you describe is what engineering is, at least partly. Your attitude, which is quite common, is why I scoff at calling what this industry does "software engineering". It's rarely as thoughtful, careful and detailed as engineering requires.
Not that that is a bad thing. Often what a business in this industry is making just isn't complicated enough to need much beyond simplistic hacking at a terminal.
Sometimes "small improvements" have ramifications outside of the context of the change (potentially significant ones). The person implementing these improvements has to understand the scope of the change (including side effects on external systems, if any), and that effort should be documented somewhere or at the very least reviewed by peers for correctness, especially for truly mission-critical or sensitive systems.
It doesn't have to be a "fill out these forms in triplicate and don't forget the new cover on your TPS report mmmkay" kind of documented effort: it's not one extreme or another.
As your company grows from small-sized to medium-sized, your technical processes need to grow, too.