I have found a post where the grid size in the Grid Tool can be update using an interface tool -- which is really wonderful.
What I would love to see is the grid size text entry box being able to accept a field name/variable, so that this can be modified without needing the interface.
This would be useful because I have users uploading shapes to be analyzed -- they don't necessarily know the size of the shape so I would rather the grid size be automatically calculated based on the square mileage of the shape.