Wouldn't it be great if you could foresee your mood? How you will be feeling tomorrow, next week, or even after an hour? You could plan everything accordingly, or at least have one serious factor to consider before committing to certain activities, making decisions and agreements in advance.
Moreover - if you could know which days will be more productive for work, which better for social interactions, creative performance and which are just best to be spent calmly at home, everything would fall into place much more smoothly and the quality of your life would increase.
The whole societal structure could be reorganized in that manner - instead of working certain number of hours each day, a person could work more on days or hours in the day favorable for work and be free on those where he/she is less productive because of the emotional status and instead do something else, to which their mood is most favorable at that time. Now we are mostly in the mercy of blind chance regarding this.
What if mood is a neurophysiological pattern
Human psychology is a complex phenomenon and the first and major objection to the notion that a person's mood can be predicted is that it seems greatly dependant on external circumstances - did you have a successful day, did everything went as planned? Maybe you got promoted at work or did you instead got stuck in traffic and had this bad quarrel with your partner, etc. Since our mood seems to be largely dependant on external factors that are virtually impossible to predict, it might appear that mood is also close to impossible to forecast. But it isn't quite so.
While it's true that events in our life influence the mood, the opposite is even more valid. The circumstances might stay more or less the same when considered objectively, in fact, they rarely change significantly in an average person's life, but our mood does change significantly and frequently. Circumstantially similar day might at times be perceived as good and at others - bad or average without much objective reason.
The very definition of mood distinguishes it from emotions and feelings because of its greater stability and tendency to linger. Our mood seems to be determined more chronologically and physiologically rather than circumstantially.
What I'm suggesting here is that each individual's mood swings might follow a distinctive pattern that could be predicted once enough accurate data about those changes is acquired. With the help of AI-driven data analysis it should be possible to separate the fluctuations of that part of our emotions which has little to do with external circumstances and follow its own independent pattern. Once this pattern is determined the mood could be predicted with a certain probability, similarly to how the weather is currently forecasted.