[Tagging] usage of maxspeed:practical is described as recommended on wiki

[Pieren]

I would modify the section [1] by replacing "it is recommended" by "it
is suggested" and adding at the end a note saying that a large part of
the community consider these two tags -smoothness and
maxspeed:practical - too subjective.

Pieren
(I also suspect the 12000 coming from some imports. Such numbers do
not say many thing if we don't know how many contributors really used
it).

[1] Marking surface of road with tag surface without adding it to
parallel roads (or adding only tags surface) may lead to unwarranted
understating priority of road relative to surrounding[1]- so it is
recommended to add also proposed tags smoothness=* and
maxspeed:practical=*.