I like to play Pokémon at competitive online play. Though singleplaying may have many key events for competitive playing. (Like the Mega stones, TMs, etc.)
Per passengers/friends you can receive additional advantages, such as O-Powers. So if you care about your friend list, it's more likely to receive these powers.
But then I'll have to ask myself: Is it better to look for as many random and foreign friends as possible or to just keep local friends in the list?
I will not have many local friends, as I'm too old for this shizzle, but I understand that they may give more powers, as we know each other. Foreign people may share a power once in a time, but as they will have other random friends it's not likely that I'm the one who receives it. On the other hand - the more foreigners I've got, my chances increases.