I mostly use speckit, not openspec. I think basically these are the same tools. There are other reasons for using such tools, but one reason is to enforce discipline for me and the LLM. Otherwise, often it starts going round in circles. Helps me save tokens as well. Again, the discipline is the important bit (along with clearly produced artefacts). Can I do all of this just with the LLM? Yes and that's what I did but it was very messy.