Question: I have plenty of *grease pencil* sketches in my blend file. Is it possible to remove all of them very fast?

Answer: 
**Short answer:** 
Yes!

Press `N`, go to *Grease Pencil* and uncheck the checkbox:

![enter image description here](https://i.stack.imgur.com/qFEgx.png)

This will hide all grease pencil sketches, while retaining the information in case you want your sketches back at a later time.

**Long answer:** 
In the *Viewport* press `N` and go to the *Grease Pencil* portion of the menu on the right. 

![enter image description here](https://i.stack.imgur.com/15bYg.png)

There are several ways to remove a grease pencil sketch, you can just hide the grease pencil (the checkbox), you can delete a frame, you can delete a layer (the "X"), or you can hide a layer (the eye).
You can use the `RMB` or use `Shift`+`D` to get the grease eraser. Use the `LMB` (or `RMB` depending on the method) to erase, and the `MMB` to change the size of the brush.
You could also run a script to remove the layers after saving the .blend the sketches should be removed.

```
import bpy

for g in bpy.data.grease_pencil:
    for l in g.layers:
        g.layers.remove(l)

```