Is there really a benefit to a person who gets a black belt in a variety of systems?

Yes. No. Did you expect me to answer it any other way. I have practiced Isshinryu for about 32 years as a black belt. I am familiar with other systems yet I felt instinctively that trying to take on more systems to lay claim to more black belts just would not work for me. In that I feel very lucky.

Also, I have done so with my system yet even now realize that I still have not learned all the principles/fundamentals of the system and/or those of all martial systems so how can I achieve a black belt in several systems in such a short time.

I had to take note of Marc MacYoung's comment about the system and its uniqueness of movement. To learn that and then several others along side it in short order seems to me to be a very tall order for even the best of practitioners who have natural ability, etc.

I guess that what I am saying, for me anyway, is that I am very lucky I couldn't fall into that trap and that I remained within my core martial system and continue to expand on it.

Yes, there is a benefit if it is merely your assimilating the system as a familiarization. No, if you are not fully encompassing all the systems principles, both martial in general and system specific, then your just adding a lot of different hand and foot movement that runs on your core system.

Lets not forget that in order to make all these systems available and applicable to combative aspects it takes a lot of work to encode it all adequately into the brain so it will actually work. That in itself says a lot cause it takes a lot of effort and time to achieve that natural and instinctive encoding, i.e. changing/adding to the minds neural pathways/networks, yes?

This then begs the question, why do it? If it is what I think, then it is merely a way to fluff up the martial art resume. Yes, I suspect this post, as many of my past posts, will "piss off" a lot of folks who have lived and achieved fame on having this or that many black belts in this or that many systems.

If you wish, won't hurt my feelings, to say that my disparity is simply jealously cause I never did or never could do the same then have at it.

p.s. Personal thought, once you have really, really learned your system then to achieve total understanding of another would require the same dedication and time so in a lifetime, to my view, you might be able to actually learn two systems ...

p.s.s. Oh, and truthfully can the brain/mind actually keep the two apart, i.e. not inadvertently as the brain does, meld them together. Can one do this with out the full time and dedication?