I'm not sure myself either, as it isn't exactly clear. The images are still there though.
What I understand is that this module uses GEOS unless it is not available, and the commented docs only apply in this case. Having beautiful illustrations appear when skimming through, but that don't apply most of the time might be misleading.

That doc was changed 9 years ago in cfd4808#diff-ac9836873e08c679bbe410bce6413b8facf60c84f0e08c83e30a8e5cc0019ccbR24-R57 from @landam and seems the images were added there.

Who uses GRASS without GEOS these days? Perhaps the commented paragraph and the images it references could be deleted.

But if this use case is still considered relevant, then the commented part, together with the "For advanced users ..." paragraph, could be put together at the end as a section apart.

@echoix perhaps we can leave this little question for the future, merge and close?

I'm also fine with this, I hoped someone would've jumped in. For docs, I really believe that PRs that improve even just a bit should be merged really quickly, as long as it doesn't regress, they should always be welcomed and merged in a timely matter.