What's the disadvantage of Extra Tunings?

People playing the harmonica have to exercise certain blow-draw patterns, combined with the movement from one hole to another, completed by pushing or releasing the slide (in the case of a Chromatic).
Those patterns are not something you think about, it's a reflex action and follows the eyes when sight-reading a score or the inner melody when playing by ear.
Another note arrangement on the instrument however, will immediately destroy your trained context, it's the same as losing a language. Those who believe they may reach their musical target faster by using an extra tuning will probably achieve some interesting effects. However, it's more the case of the harmonica playing the player than the other way around, as it should be.

In the end you'll discover the amount of differently tuned harmonicas you have to carry with you has increased tremendously, the more different tunings and keys you use. Onstage, you will appear as a harmonica searching monster, always rummaging in your enormous suitcase. The audience will remember you as a self-centered, strangely averted creature and not as a relaxed, entertaining person. You may hold the opinion that public opinion isn't important anyway, in that case you may ignore this sentence as well.