Research has shown that separate neural pathways to the brain exist for tactile impulses and visible/audible information which is why musicians find that tactile pulses are quickly internalized, allowing them to concentrate on reading and listening to the music without the constant distraction of an audio or visual metronome. Feeling the beat, not having to listen to clicks or look at blinking LEDs makes it much easier to focus on the music and playing in correct time.

What’s the difference between a regular metronome and the BodyBeat?
Sophisticated metronomes can produce two or more distinct sounds. A regular "tick" sound indicates the beat within each measure, and another, distinct sound (often of a different timbre, higher pitch and/or greater volume) indicates the beginning of each measure. A tempo control adjusts the amount of time separating each beat (typically measured in beats per minute), while another, discrete, control adjusts the meter of the rhythm and thus the number of beats in each measure. This number is an integer often ranging from one to six, though some metronomes go up to nine or higher.