IMO the most important practical difference between P2P and P2NP is the fact that P2NP can be directly reduced to Amphetamine with the use of a suitable reducing agent while P2P is lacking the nitrogen and needs to undergo reductive amination reaction for amphetamine (or methamphetamine) synthesis.
P2NP can be converted to P2P in fairly good yield with easy procedures If you either don't have access to needed reducing agents and want to go for the leuckart Method instead or If you want methamphetamine as your end product.