So many excellent reasons for making a grisaille.
Let me name a few:
1.I use it to figure out the shapes.
2.Since color is not a pieces of the puzzle it's easier to change things .
3. If you can't make the mood in value, you have no chance in color.
Reasons to "remove it."
Keeping allows the dark to have more color and is somewhat easier to keep transparent.
The value are noted for reference, yet you aren't completely wedded to them.