With open world games it becomes very evident when developers include activities just to make the game not feel as empty. You can usually tell because these activties are simple, boring, and there are an abundance of them.
For open world games to be fun, they need to have side actitities that make sense for that world. One of my biggest complaints about ME:A was how boring and reptitive the side content in the game was, and despite this, the game still felt empty as hell.
That is why in some games and in side quests, we meet some characters and sometimes, the characters try to catch the player's attention to remain as Easter Egg. Although in general the secondary missions are usually people asking us for favors.