My personal experience is that the board game apps have convinced me to purchase the real game. It is a great way to test games out before dropping big $$ to get them.
I've never played Pandemic, but I'm expecting I'll enjoy it in the app and then invest in the real game (and probably the expansions).
This. Playing the app makes me want the game. The board game apps are great, but they just can't replicate that board game experience.
I've gotten into Small World, Memoir '44, Elder Sign, and Ticket to Ride based on sampling iOS or steam versions of the games. Pandemic is now on the want list