What are the benefits of using an overhand grip?
The tripod grips are used mostly for drawing &quot;lines&quot;, whether plain writing of text, or drawing contours.
However, the overhand grip is used mostly for filling areas, e.g. backgrounds. This grip keeps the tip away from the drawing surface, allowing the side of the pencil (or drawing tool in general) to contact the paper. The result is a more uniform spread of the &quot;color&quot;.

Which joint should I mostly be using with an overhand grip? (wrist / elbow / shoulder / a combination).

It depends on the several factors, e.g.:

your position on the chair;
the size and shape of the drawing area;
the specifics of the &quot;pencil&quot;;
what is comfortable for you;
what result you want to get; moving different joints results in different spread of the &quot;color&quot;;
others.


Is this grip practical for painting? (or is it exclusive to dry medium)

It depends on the brush. If you use normal brush and any tripod grip, applying slightly more pressure results in the hairs bending and getting a result similar to the overhand grip.

Are there other benefits to using an overhand grip, apart from large flowing strokes?

Painting related: A special situation is when you need to add color inside a large, still wet area. In that case you will probably rest the wrist somewhere outside the painting, and use an overhand grip to apply the color to the desired area. If you need to draw a line in this situation, then it is quite likely that you will need to use a very thin brush, maybe even one with a bent &quot;neck&quot;.