They allow the painter to draw or paint directly onto a surface without brushes, palettes, paint tubes or solvents. To a limited extent, these same qualities are also found in oil pastels. However, there are significant differences between the two.
Oil pastels employ a non drying oil and often a higher proportion of wax.
As a result, they are less a paint than a drawing medium. Oil pastels are more resistant, do not readily build up a paint mass, and will not form a durable film. Work done with them must be glassed, and this confines the scale on which that work can be done. Oil sticks will dry to a durable film, so that work done with them does not need to be glassed. They can therefore be used, like any oil paint, on work of any dimension.