macro related-labels can be used as a navigation element but needs adaptions

First of all: the macro doesn't behave as expected. It's documentation says: "List the related labels for a given set of labels, or for the current page"

I understand related labels as following:
The relation between labels exist since they are attached on the same page describing either a topic (e.g. quality, improvement, software_confluence, ...) or a type (issue, meeting-note, abbreviation, security-bulletin, ...) There is no hierarchie so that's the only relation implicitly given. If I enter one or multiple labels into the macro parameter then I expect to see all labels that are attached to all pages carrying this one/these multiple stated label.
The current output is designed with a different understanding so it actually works correct to your concept. BUT it has operational weaknesses!
How it works now:
SELECT all labels FROM all pages WHERE pages have ('label1' OR 'label2' OR ...)
How it should work:
SELECT all labels FROM all pages WHERE pages have ('label1' AND 'label2' AND ...)

This has to be understood:

• With 'OR' one gets all occurances of labels. If one enters more labels the list increases. This functionality therefore gets less useful the more content develops. That's why I suppose this macro to be rarely used (check it in your cloud and state the result, I'm highly interested): It deliveres too much lables increasingly related to the amount of content.
• With 'AND' the number of labels decreases with every added label. Principle: reduce to the max. with potential for fuzzy topic-based search.

How to improve:

1. output related labels of pages containing all stated labels using 'AND' in the select statement. One can decrease the amount of labels using more labels in the parameter and then reduce this amount again with another label and so on.
2. Allow choice of outputting 'list' or 'heatmap'. The heatmap indicates with it's size another information useful for searching.
3. Allow choice of space (empty=all spaces, @self=current space, one or more spaces). That enables space navigation or topic-oriented navigation within a wikipage itself.
4. if one clicks on one of these labels then without page reload the new label cloud is delivered and the selected label is shown in a separat list of 'selected labels' as well as the number of (visible) content items that contain all selected labels. If the user clicks on the number of content items then these are displayed for him to choose (which then actually can be connected with a page reload).

Recommendation: This macro should be used in the space navigation as an option to the page tree and on the site-search (if you adapt these suggestions one can use it also as a better topic navigation). When you click a label the label heatmap reloads and the labels shown are dependent on the label(s) clicked before. If one has the interesting labels then he receives the result pages. We can have a conference to talk about that idea in detail.

With this you'll lift label usage. I am sure! And this will work better with increasing page count within a space since the hierarchies weaknesses grow with the size of a space! Prepare for the future.