Hubs are different locations in the game that serve as your base of operations throughout the story mode. Inside and outside of story they are safe locations where you will not be attacked or engaged in any combat. Hubs are also where you can find all the vendors. The only exception is that Odin's Palace has some vendors none of the other Hubs have. It should also be noted that whenever you are inside a Hub any current boosts you may be using STOP COUNTING down as your time against you. All boosts are "paused" while inside a Hub. (Note: The bottom floor of Avengers tower if you take the elevator down does NOT count as inside the Hub). They can also be used as social areas to meet other players form groups and/or Super groups.