Drawing is a common medium for all visual artists.
But have you thought that there might be different styles of drawing; depending what medium the artist works in? As sketching is a common purpose for all artists in order to make logs of what they have seen, or just references to subjects that they are studying at the time; or for their new subject.
Drawings for a sculptor differ than that of two dimension artists that mainly work on a flat surface like canvas.
Sculptures don't work in two dimensional formations or spaces as you could call it.
And don't need to spend time on developing complex systems of perspective of say..
..
crowded scenes or landscapes as other artists do.
Indeed studies sketched by a sculptor are more lightly to be self-contained within a picture plane.
And may range from the simplest to the most complex of examination of a subject.
Colour plays a less important role in a sculptures life, as they mainly work with same colour masses.
Since for the sculptor; is to define in three dimensional masses.
Without the need of using colours to express, the sculptor will in turn work with only a few colours when doing reparation drawings.
As the sculptor plays with surfaces and the way light will play with the sculpture itself.
Drawing reference drawings, brings forth many different dimensions of their subject that they will eventually be sculpting.
I myself will also use reference books, look for the subjects that I want to use in my sculpture and have them strewn about me on the floor and the tables as I work.
So as a sculpture, you need to concentrate with detail and flow of your drawings, not colour and the expression of tone that brings to life the works of two dimensional artists.
For good reference you can also go and have a look at some of Leonardo Da Vinci's drawings and also the different style of Rodin.