1. Yes; if the protasis (the if-clause) is very long, and contains many convoluted clauses (perhaps with parentheses; or even parentheses within parentheses (not that one should encourage nested parentheses)), or perhaps even additional if-clauses (protases), if your taste runs to such things, then yes, a "then" can serve to notify the reader that the apodosis (the main clause) is at last about to begin.
2. Yes; the "if X, then Y" structure can be used to emphasise the dependency of Y on X; though it may bring with it a whiff of the "if p, then q" of Logic.
(In ordinary usage, by the way, "If X, then Y" doesn't necessarily have a sense of "If and only if X, then Y".)