Can be used for lineart or sketching!! :O
The brush relies on pen pressure for it to be more visible. Examples of the different pen pressures are:

Low Pen Pressure
- Soft
- Low Opacity
- Build it up
- For fine detail
Note: If you want it to remain the same line weight but wish for it to be darker, copy the layer of the low pen pressure and paste it till it becomes much more visible.

Normal Pressure
- Can build up opacity
- Preferred for sketch
- Much more easy on the hand

High Pen Pressure
- Darker
- More visible
- Suited for borders of lineart or thicker lineart
- Use for bolder artwork or stylistic text
You can also use this brush as an eraser!

For people who have their keyboard as the alphabet, press C or click this under where you change the colors to enable eraser mode

Pixel Sizes:

An example of how I used this brush with this illustration!

If you zoom in closely, you can I use all sorts of pen pressure here!