By overriding tools, you can increase productivity by rapidly switching between tools used for short tasks and your previous tool.
Most drawing tool shortcuts are accessed using the [Alt] key followed by another key, such as the Eraser tool which is accessed by pressing [Alt]+[E]. If you are drawing with the Brush tool and need to briefly switch to the Eraser before continuing, hold down the [E] key while you erase. Once done, release the [E] key to return to the previous tool, in this case, the Brush.
You can do the same for most drawing tools that have a shortcut comprised of [Alt] followed by another key.