I've never used anything on any of my guitars, basses, keys or drums. Various fingerboard essences (all wood...), and some over fifty years old, now. No sign of issues with any of them. I think it depends somewhat on one's climatic conditions (high and rapid humidity and/or temperature swings...); in the UK or here in France I've never had, myself, nor any folks I know, problems. I have used Dr Duck's wax for cleaning, on occasion on some (rarely...), though. Things might be different for other instruments, such as db, clarinet or oboe.