The documentation does not (or should not) say to do this any more,
as this has NOT been true since the release of SketchUp 2014.
If you find documentation that says this online, please report it, in the following category:
Meta : Help Center - Report a Problem
As Dave said, with the release of SU2014, which switched to running Ruby 2.x, finally Ruby had unicode character support, which allowed use of unicode characters in path strings, which allowed the user plugins to be moved into the user’s %AppData% folders (where user data belongs.)
With recent releases (2017) more and more of SketchUp’s user data is being moved into the %AppData% folders (ie, Materials, etc.)
You should take some time to catch up with the Release Notes page:
SU up thru version 7 used Ruby 1.8.0 on PC. (various newer versions on Mac.)
SU 8 and 2013 on PC used Ruby version 1.8.6-p287 (but v 1.8.5 on Mac.)
SU 2014 - 2016 finally both editions (PC and Mac) ran Ruby 2.0.0-p247.
SU 2017 runs Ruby 2.2.4-p230.
Most breaking changes happened between the 1.8 and 2.0 trunks.
So good search terms are: “ruby breaking changes”
I posted links to the change files from the Ruby source repositories in this post: