The emotions expressed by humans can be divided into two broad categories. We can regard them as polarized, as opposite of each other, or we could just say that there is a dividing line where one type of emotions change into the other type of emotions.
We can call the two types of emotions Negative and Positive. That is not so much as value judgment as it is a description of the main action of each group. Judging either as "good" or "bad" isn't very helpful.
Negative emotions express an attempt or intention to Exclude. Strengthening one's own position at the expense of others. Keeping bad stuff away, destroying what is perceived as a threat. Negative emotions are fueled by an underlying fear of the unknown, a fear of the actions of others, and a need to control them or stop them to avoid being harmed.
Positive emotions express an attempt or an intention to Include. Taking the whole into consideration. Working on learning more viewpoints, interacting more with others, enjoying making things better. Positive emotions are fueled by an underlying desire for enjoyment and unity.
Negative emotions are, for example: apathy, grief, fear, hatred, shame, blame, regret, resentment, anger, hostility.
Positive emotions are, for example: interest, enthusiasm, boredom, laughter, empathy, action, curiosity.
There is a range of different emotions in each category. We could say that some are more positive or negative than others. But it isn't necessarily practical to place them on a linear scale, since each one is a composite of various elements.
Some emotions camouflage as positive or negative, but really are the opposite of what they pretend. There is a type of pity which appears as genuine concern for others, but which is rather taking comfort in that somebody else is worse off than you. There is a covert hostility that masks as friendliness, which can often be difficult to assess at first. Likewise, some kinds of anger or tears might look negative, but might really be an expression of involvement and care for the whole. It is the underlying mechanism and motivation that counts, more than the superficial outward manifestation.
It might sound like the negative emotions are just something to get rid of. It is not that simple, however. They serve important functions. Basically they show that there is something one doesn't know and can't deal with. If that becomes motivation to then learn it and deal with it, that is very useful. If one is always joyful, one might miss noticing things that are wrong.
Positive and negative emotions are polarities. We can't get rid of one and just keep the other. Ultimately they need to be integrated.
Typically, negative emotion in a client will point us towards areas that need to be processed. They show that there is something there that the person isn't dealing with. We would make her deal with them and transform them into something more useful and enjoyable.
The negative emotions are useful as motivation for moving away from what one doesn't want. The positive emotions are useful as motivation for moving towards what one does want.
Trouble enters when parts of the system get stuck. Particularly when the functions get reversed and the person starts moving towards what she doesn't want. Therefore, stuck negative emotions are a prime target for processing.
People might express all sorts of combinations of these emotions. Some people will be fairly chronically stuck in a negative emotion, like grief for example. Others might be stuck in a positive one, like contentment, and won't be able to experience negative emotions, even when appropriate.
Others will in stressful situations react according to certain emotional patterns. Like, a person might have hidden grief or fear that gets triggered by certain circumstances. A casual remark might push a button that unleashes pent-up anger.
The aim in processing is to make people more fluid in terms of emotion. Able to use whatever emotion is most appropriate, and being able to use the full range as necessary. Most likely a person who is fluid and flexible will choose to live mostly in a positive frame of mind. But the goal is actually integration, moving beyond the positive/negative idea altogether.