Someone without the ability to experience physical pain doesn't know when in a dangerous situation: bones get broken, skin is burned. Acute physical pain serves a function by letting us know when we are in an unsafe situation or something is askew within our bodies. When that signal is turned off, greater problems ensue.
Similarly, negative emotional states serve as cues. They indicate that something in our internal or external environment is off. When angry, we look to where we are not being served honorably. When scared, we look to what is causing the fear. When we don't allow the entire constellation of emotional states, we cannot know when something is off. We also will struggle to know when happy if sadness is not allowed. It is key to first gently label the emotions, positive and negative, with nonjudgmental curiosity. Then we determine if the situation is controllable or not. If we can modify what is causing anger, fear, sadness, take action! When the situation is out of our control, reduce undue suffering by accepting the situation even if not with approval. We can never actively remove any emotion, not like turning off an electricity switch, but we have the capacity to change our relationship with that emotion.
The emotion can become the bad guy when it serves on its own and drives poor behavioral choices. An elegant New York Times article from November 4, 2014, entitled "Emotion is not the best medicine," looks at this. Jane E. Brody, in the context of the Ebola crisis, discusses problems when people rely on fear as opposed to fact. This is true. It is important to take the emotional response as a cue but to not rely on the emotional response for what is done next. Emotions are not fact. This is even more difficult to parse out when physiological responses happen in relation to the emotion: responses like increased heart rate, flushed cheeks, common with emotions related to anxiety, cement for the individual that the emotion is fact. Brody addresses studies that indicate that "people are more fearful of things they can't control, however remote the risk may be." This is seen with the Ebola crisis. This is seen with fear of flying where, factually, risks from flying are much lower than from driving. Take the emotion is a cue to explore the situation further and use both the data and the emotion to drive decisions.
The limbic system, in the subcortical portion of our brains, houses the amygdala where much of our strong emotional states are concentrated. A New York Times article, "Restoring a Master's Voice," by George Johnson, dated December 23, 2015, starts with looking at our limited view of Ivan Pavlov's work. He did not simply want to explore why dogs salivated. He wanted to look at theory of mind and illuminate consciousness. Over a century later, with tools more elegant such as the fMRI and PET scans and micro electrodes, we still do not grasp what drives scientific creativity or curiosity in the arts and literature. We still don't grasp how people faced with opposing forces unable to find resolution then break down.
The science will become more and more elegant and probing. Until then, I would argue that the most useful nugget is to come back to labeling and accepting our emotional states, labeling and accepting the data even when encompassing both thesis and antithesis. Then, from a melding of emotion and reason can come a synthesis that allows us to climb up from suffering and to climb up from a purgatory of sorts where we have sat in painful limbo unable to reconcile common opposing forces natural to the act of living.
The emotion serves as an indicator of what is going on internally and externally. The emotion, even when negative, is only problematic when it and only it drives a behavioral choice. Even not yet fulling grasping how consciousness works, what is important is to use emotion, use data, sit with conflict within each and between each, and then take our next action. This action can be the shape of change or it may in fact be radical acceptance when that change is out of our control.