The purpose of bracing is to make a car as rigid and inflexible as possible so that external forces can be completely controlled by the suspension. The suspension is designed to handle bumps, vibration, and shifting inertia as the car moves, so the goal is to bring as much control over those forces as possible to the shocks and springs. The three most popular bracing options for street Miatas are frame rails, rollbars, and fender braces. Garage Star claims their fender braces reduce cowl shake, rattle, and improve stability on high-speed turns.
This mod uses mostly existing bolt holes in the body, including the door hinge mounting points, and connects 4 different points around the wheel well to stiffen the entire fender area. The top mounting point requires drilling one hole for attaching the brace with a backing plate.
Some of the bolts are tricky, but TheCarPassionChannel has a great explanation video of this mod, which also shows where all of the bolts are to remove the fender.
The bottom of the fender is an area where debris and gunk can collect, which ends up holding water and creating rust. I did not find any rust under my fender, but I did find a pile of leaves, sticks, and dirt. Before I re-installed the fender, I protected the whole area with a layer of rubberized protective coating, and added sound deadening to the body panel.