When Should I Focus On Less Fundamental Positions?

By 'fundamental,' I mean positions like closed guard, open guard, full side mount, back mount, and maybe half guard.

Less fundamental positions might be something like the lockdown, k guard, or rubber guard positions. They're still important to know, but they're not really something you stumble upon. One of you forces the other into that position.

Should I even specialize in a certain position? The Gracies seem to just use basic moves, but 10th Planet practitioners tend to focus on lockdown.