It looks like there is some evidence that it has benefits in certain situations.
https://www.sciencedirect.com/science/article/pii/S0042698918302001
My interest in it is probably because I’m a chronic experimenter (mental exercise, food, sleep, etc.). There might not be any benefit, but experimentation can lead to new ideas. Not having the exact result as a person with grapheme-color synesthesia from birth doesn’t mean that the experiment failed. 
Also, it might be possible for people with sensory crossover to increase or manage that sensory crossover.
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