extra Storm Trooper,Tie Fighter,Immobilize, Infantry Gernade helps build better decks faster, might be a waste in the long run as you will get these in boosters
only way to get a 2nd set of F110D rifles/light sabers so you can build 2 decks using 2 at the same time
only way to get a 2nd copy of mind probe --- this is the main reason
In order of likelihood
1. Mind Probe - The only way to get a second copy without buying a single (usually for $10-12 on its own)
2. FO Trooper - If you want to run 3-4 troopers in a deck, chances of pulling 2 and especially 3 more from boxes is low. Combining that with 1 (and 3) makes this a better deal.
3. F110D is a great card in many scenarios.. you DO end up with 2 copies between both starters.. but yeah if you want two complete decks, and already bought a second Rey starter.. then a second Kylo one will give you two playable sets.