Traction limits what a single contact patch will support in braking: loose/broken/wet surfaces can require the use of F&R to avoid a lock-up and maximize control.
For experienced riders the application of front or rear brakes can have different functions other than just short stopping distances.
Setting up for corners, keeping the correct distance in a paceline, covering a brake while reaching for a drink or descending at pace require different modulations.

FW bikes require properly set-up brakes F&R.

-Bandera