Please, don’t extrapolate from your personal preference to a general principle: it serves no purpose, and you definitely can’t know that. Reasoning by absolutes, in UI design, is never a good idea.
The reason why some volumes have been moved to the Others section is because having a lot of elements in the side bar—which can grow arbitrarily large, with the various user directories, remote volumes, and user shortcuts—is not going to be helpful either. Saving one click is not a design direction: we are not trying to speed-run the desktop experience.
If you want to always have access to some locations from the side bar, you can use shortcuts. You cannot hide the “Other locations” button.
What’s a “testing” phase? The current UI of Nautilus has been there for the past few years.