Sideways

 Here is one of those topics in martial training that tends to be divisive, although it really doesn't need to be. See, in the traditional arts there is often a lot of emphasis on practicing any and all techniques on both sides equally, with the declared ideal of becoming ambidextrous in application. Let me state it right here -  I don't think you can ever become truly ambidextrous from training, no matter how many sinawali patterns you happen to learn...however, becoming bilaterally functional is another thing. 

But, let's take a step back. For the opponents of the idea of bilateral training, since most of us are not professionals in the field and don't have all the time in the world to only focus on training, the limited time we do have on disposal ought to be dedicated to developing the best possibly performance ability on the preferred side. Interestingly, the professionals, who can and do dedicate their lives to training, for the most part also firmly belong to this camp. After all, how many boxers do you know who can switch stances fluidly and box equally well on both sides? It brings to memory an old interview of Bill "Superfoot" Wallace, the legendary full contact champion, who only kicked with his left foot. Namely, asked about that he said that faced with a choice of having two good legs (if not mediocre) or one that is unstoppably phenomenal, he chose the later. And from the standpoint of a competitor whose belt is on the line, it makes sense. After all, symmetry is not even natural, right?

Hmmm...

But, what about those of us who aren't high level competitors, so no big money or titles on the line? Plus, the self-defense oriented community resorts to the argument of defending when your strong/dominant side is injured. And before some of you laugh an point that if the opponent is good enough to eliminate our string side option, the other will be a joke, let me point out that not all injuries are incurred in an encounter as such. For example, I am currently boasting a bad case of tendinitis in my right wrist, unrelated to training, and I'd rather train with my left than not at all. 

That said, it is not even the main benefit I see in the bilateral approach. The biggest advantage there is to it, lies in the fact that such endeavor shows strong benefits to the maintenance and improvement of the overall neural and cognitive systems. Creating new neural pathways, firing synapses etc, it all has long term good effects on human health and functioning. 

Since the work on the non-dominant side essentially stimulates the "opposite" side of the brain, typically related to creativity and intuitive thinking, this might even enhance one's ability to find new solutions to the problems faced. The maintenance of the neural and cognitive networks as also VERY important in the advanced age, to prevent dementia and other degenerative issues. 

However, we don't even have to go into brain science to see other, possibly more evident upsides. Depending on the chosen training discipline, training exclusively on one side may lead to an unbalanced muscular development (particularly when training with heavy implements/weapons), which in turn results in problems with posture and movement patterns, further loading the compensatory joints and movements, and the injuries that will stem from that. 

By the way, if you also include regular conditioning work in your training process, such as weight lifting, roadwork, intervals and so on, would you approach that work with emphasis on the dominant side only? Yeah, I though so...

There is a kind of a third way, too! Years ago, I talked to a pencak silat instructor about this subject, nudged by his "don't care" attitude about whether the jurus of his system (forms) should be practiced in the mirror image as well, since they are not symmetrical on their own. His response was that that a practitioner could develop two different sets of responses for the attack coming on similar lines but from two different sides. I found it awkward at the time, but later it started making sense. Again, going back to weapon-based systems, you just have to work this way! Well, unless you switch the tool between the two hands or grips to deal with the stimuli from left or right. 

In conclusion, I'm afraid there is till no definitive answer to the debate, but hopefully you will find some information here that will help you organize your training better, according to your own needs and priorities.