This is a very good question. There are a lot of possible and good answers and you can argue, that the right solution is more of a style than a discrete description. But I am trying never the less:
- Try to create as little spaces as possible.
- Having one central big space open for everyone to view, edit and comment may feel awkward for a lot of companies but is the right way to go. Try it, even if you are suspicious.
- If you need rights restricted constantly and systematically this is a strong sign for a separate space. Doing this in a space tree is always a hassle and adding unnecessary complexity.
- I advocate for letting everyone create spaces but heavily question spaces that can be merge. It is extra work though.
- It is common, that users create separate spaces for just about every topic. If you do not need to be space admin or have any rights management reason, the space could probably be dissolved. If you have more than 100 pages (or pick a number that suits your company), that justifies another space.
Does this help you?