Re tailskids versus tailwheels--
Tailskids are inferior to tailwheels for directional control on hard-surfaced runways, even if said tailskids are steerable. Of course this is a negative advantage (disadvantage), not an advantage.
(Re steerable tailskids-- see https://en.wikipedia.org/wiki/Conventional_landing_gear )
Especially on a grass or dirt ...
"Wheel pants" is a common term for these wheel fairings, at least in US usage, which serve to reduce drag. They have also been called "spats", though that term has traditionally been reserved for something much larger, at least in US usage.
How can drag induced by the landing gear be reduced?? -- see all answers
What is "spatted ...
Those are called speed fairings.
They make the shape over the tire more aerodynamic and reduce drag, thus increasing airspeed and fuel efficiency.
This is a page in a Cessna 172R information manual that comments on the differences in performance when they are installed.