1. Earth Will Be More Vulnerable
The fact is, without Hulk and Thor, Earth is a hell of a lot more vulnerable to attack than it is with them there. This is something that won't go unnoticed by the likes of the Mad Titan Thanos, who may well plot his assault on the planet based on their absence. Nick Fury specifically stated that the events in The Avengers will have made other worlds take notice that Earth isn't to be trifled with - but with two of the biggest guns off-planet (as it is believed that Hulk is venturing towards Asgard somehow), he may well strike on that basis. Avengers: Infinity War is likely to start without Hulk and Thor, with their return (perhaps in the second movie) symbolising the start of the heroic fightback. Don't be surprised to see Thanos appearing in a Captain America: Civil War mid or post-credits scene indicating that he is ready to make his first move towards Earth based on its vulnerable state.