Many times, when the subject of cross training comes up, people often say that its not necessary, because there is more than enough to focus on in a single art. By doing more than one thing at the same time, you're taking away from the base art. You're taking away from being able to perfect everything in that base art.
Now, personally, I think that one shouldn't have to spend a lifetime in order to perfect something. Its not going to happen overnight either, but like I said, it shouldn't take 20 yrs. either.
Another side of the debate is when people say its better to have 5 things you can do really good, rather than 20 things that they can do fairly well. So when the mention of crosstraining comes up, thats basically adding more things, so in essence, thats more that you have to perfect.
Thoughts?
When one is beginning to learn an art, I have found that it is easier for that person (* the average person tere are always exceptions *) that they get a base in one art first before cross training. So when one instructor says do this and another says do that that they understand enough of body mechanics to understand why there is a difference and the applications or enough to ask about the applications and respect the differences and commonalities.
As to how long? That depends upon the person in question. Some will never grasp it all enough to be able to move form one to another without being confused. Others will wonder from art to art until they find the right instructor and or system that teaches them in a way they can learn and then all of a sudden their previous training will all make sense.
This is why when someone says, "so and so got their rank in 'x' years and I have been to as many classes as them and I was not able to test, ..., ", brings questions of where the person is at in their personal training. No matter how much we want to make everyone equal we are all individuals with independant strengths and weaknesses and ways to learn.
So cross training is fine to learn how others move. It also might open the door into a new matrix of learning where they can learn better for them.
I also think it depends upon what people are looking for out of their "ART"? Meaning that is one is looking for exercise then certain schools and arts will help them. Others are looking for tradition and certain schools and arts will be better for them as well. Some are for self defense, and to a certain degree they all help, but some work better than others so some arts will happen to be better for their training. It depends upon what the person is looking for and what they are hoping to get out of their training.