/sci/ - Science & Math

When I was learning proofs, I recall my professor telling me that
[math] P(n-1) \Rightarrow P(n) [\math]
was a better or more robust or more educated way to do induction proofs than
[math] P(n) \Rightarrow P(n+1) [\math]

but I don't remember how he justified that. Can anybody provide input, re: how that might be the case?