In social interactions, the more emotional party is usually the dominant one. If a friend or family member is excited, angry or feeling hurt, there isn't much question of what you're going to be talking about with them for the next ten or twenty minutes. The emotional person will demand the attention and energy of the calmer one.
If you're the calmer peron, you'll get caught up in sharing their excitement, trying to calm their anger, or soothing their hurt feelings. The emotional person isn't going to allow you to say "Let me tell you about the book I'm reading."
To the extent feelings are positive and enjoyable, that can be a good thing. To the extent that another person can push negative, unpleasant feelings into your life, that's obviously not such a good thing.
This dynamic is something fiction writers know well: feelings have a huge amount of control over what we talk about, how we talk about it, and what we consider to be important. Emotions can define what people find is most real and immediate, and even though the emotional person might be completely irrational, that person is just about always the one who ends up defining the topic of conversation.