I agree with both parts. Most people do have a "strong" side, by preference or by upbringing, but you should still be at least familiar if not comfortable with moves on both sides. I would rather be 75% proficient with one side and 25% with the other, than 100% with one side and completely incapable of the other.
Agreed. I think that learning to lazy or tic tac (for arguments sake) with your "dark side" is important, maybe even learning how to speed or kong vault. But, at that same time, I'd much rather be MORE proficient with my dominant side than the other, as that's where my comfort zone is, and that's where I will perform most admirably.
And to further the argument, "if" is a pretty big two letter word. If I came into a situation where I needed to use my left side, I would, even if I knew I was terrible with it. But I'd make the best of it, because that's what I needed to do. For now, this newbie is gonna focus on his right side. Once I get everything down fairly good, then
maybe I'll start doing some simple stuff on my left side. Until then, It's just another thing to think about training for.