As to whether or not it is a good idea for someone to go along with another person's emotional state can all depend on what state they are in. If this person is happy, embracing the same state is likely to have a positive effect on ones well being.
On the other hand, if this person is angry or even miserable, embracing this state is unlikely to do them any good. There are then going to be times when it will be a good idea for one to allow their emotional state to mimic another person's emotional state and times when it won't.
Emotional Contagion
However, even though this is the case, one may find that there are times when they are unable to control how they feel. Ergo, irrespective of what is going on for another person, they will end up being drawn in.
This is not going to be a problem if another person is in a good place, but it will be if they are not. When it comes to the latter, it might be necessary for one to get away from the other person.
A Time and A Place
This doesn't mean that one should get away from someone if they are going through a tough time. The reason for this is that there will be times when another person won't be in a good way and it will be a good idea for them to offer their support.
Someone in this person's life may have passed on, putting them in a very low place. Ones mood can then drop during this time, but shortly after their time together has come to an end, it should return to how it was.
Boundaries
Undoubtedly, having the ability to connect to another person's mood is going to have a positive effect on their relationships. At the same time, being able to maintain their state will also allow them to act like an individual.
If they didn't have this ability, they would end up acting as though they were simply an extension of other people. Instead of being able to assert themselves, they would be at the whim of other people's moods.
The Truth
Just because someone else is not in a good place or is very angry, for instance, it doesn't mean that one should join them. Ultimately, there is no need for them to feel responsible for what another person is going through; that is, of course, unless they have played a part in what is going on for them.
And if the other person takes responsibility for what they are going through, they won't expect one to act like they have played a part. This can show that the other person also has well defined boundaries.
A Different Reality
Not everyone is going to be able to relate to this, which means that there will be people that find it hard to maintain their emotional state around others. Thus, instead of being able to act like an individual, they can act as though they are just an extension of others.
If they are able to maintain their emotional state, it may only be due to the fact that another person's emotional state is the same. The other person will provide them with the permission that they need in order to experience the same feelings.
Walking On Egg Shells