I installed just a cutoff switch on the negative side for two purposes. One in case of a electrical fire, while I was in the process of replacing faulty wiring, I could quickly kill the power due to the battery being under the mat and second as a theft deterrent. It won’t stop an educated thief but will stop a kid with a stupid idea of taking a joy ride.
Another benefit is isolating the battery during winter storage.
Nice discrete install. Looks like seat frame. Does the other end of that ground go to the chassis or a bell housing/ starter bolt?