Triming
The slicing tool is very useful in digital sculpting because you can't simply use a brush and flatten a surface on your computer. Every shape ypu work on has a mesh and it is a geometric pattern on the surface of the model it is made up of squares or polygons and they don't magically multiply as you sculpt and you need them. However when using a slicing tool on digital software most of it will ignore the polygons cut across them and close the cut with voxeled polygons for cleaner edges.
Resolution
On the topic of polygons comes resolution here you can see the mesh on my model and it is made of little squares as I move the resolution slider the mesh shrink creating more square. In other words as I sculpt i'll have more resolution and detail to work with. However there is a limit and so you don't want to use it at the begining when you are just sculpting like detailess shapes.
Masking
So up to this point digital sculpting sounds more complicated than traditional, and you're right to a certain extent it has a steeper learning curve you can't just push around the model in any shape you like. But it comes with advantages that you can't do with real clay. One of those is masking, you've probably heard this term in painting where you mask with tape an area of an object you don't want to paint and then paint without a care knowing the masked area will not be affected. Similarly in digital sculpting you can mask an area and the geometry there will remain unaffected you can even hide the mask area so that you can see the inside of your model and sculpt inside.