Where I work we tend to write RFCs for fundamental design decisions. Deciding what counts as a "fundamental design decision" is sometimes self-moderated in the moment but we also account for it when making long term plans. For example when initially creating epics in Jira we might find it hard to flesh out as we don't really know how we're going to approach it, so we just start it off with a task to write an RFC.
These can be written either for just our team or for the eyes of all other software teams. In the latter case we put these forward as RFCs for discussion in a fortnightly meeting, which is announced well in advance so people can read them, leave comments beforehand, and only need to attend the meeting if there's an RFC of interest to them up for discussion.
This has gone pretty well for us! It can feel like a pain to write some of these, and at times I think we overuse them somewhat, but I much prefer our approach to any other place I've worked where we didn't have any sort of collaborative design process in place at all.
I view this process like this:
code review is a communication tool: you can discuss concrete decisions vs hand waving and explaining in the conceptual space, which of course has its place, but is limited.
But writing the whole working code just to discuss some APIs is too much and will require extra work to change if problems are surfaced on review.
So a design document is something in the middle: it should draw a line where the picture of the planned change is as clear as possible and can be communicated with shareholders.
Other possible middle grounds include PRs that don’t pass all tests or that don’t even build at all. You just have to choose the most appropriate sequence of communication tools to come to agreements in the team and come to a point where the team is on the same page on all the decisions and how the final picture looks.
These can be written either for just our team or for the eyes of all other software teams. In the latter case we put these forward as RFCs for discussion in a fortnightly meeting, which is announced well in advance so people can read them, leave comments beforehand, and only need to attend the meeting if there's an RFC of interest to them up for discussion.
This has gone pretty well for us! It can feel like a pain to write some of these, and at times I think we overuse them somewhat, but I much prefer our approach to any other place I've worked where we didn't have any sort of collaborative design process in place at all.