So many people thing that training in multiple styles of martial arts is a bad thing, or a forbidden thing, something that is just plain wrong. In all honesty, I don't see why. Personally I have trained in karate my entire life. However, my sensei was always teaching us small parts of different styles of martial arts. Over time, those small things actually became part of our curriculum.
I grew up with karate being the main focus but we learned Judo throws, Taekwondo forms, kickboxing techniques, Aikido manipulations, Kung-fu strikes, weapons fighting, and Ju-jit su locks and takedowns (see the next blog post).
Why did we learn all this? My sensei has a firm belief that not matter what base of martial arts you train in, they are all tied together and can be used across the board. For example, sometimes people find themselves in a situation where they have to make use out of the things around them. While this things may not be a sword, nun-chuku, said, or a bo, when you are trained to use those weapons, it becomes easier to use a broom stick as a bo, a towel as nun-chuku, and so on.
Now I know that sounds very "Hollywood" and too much like a scripted movie, but the fact is, these things happen in real life. There isn't always room for perfect blocks and punches. Sometimes we have no choice but to grab a joint and get the person on the floor, sometimes we are to close too throw a straight punch and we need to throw an uppercut or hook punch.
This is why cross training is important, at least a little bit of it. Karate may be perfect as a self defence against another karate practitioner, but the reality is that if you get into a fight, the person your fighting has zero karate training. Fights don't go the way we train for them in a class setting. That's just a fact. This is why I will never stop my students from exploring different styles of martial arts, or from training at another school of a different style.
This is also why when I get new students, if they have a belt from a previous school, they keep that belt. Those students earned it and I would never strip that from them. However, it is on those students to learn our curriculum up to that belt level. From there they will progress through our system.
In my personal opinion, cross training is a good thing. Cross training is important.