Crying lowers stress for whatever complex neurochemical reasons. Could be an accident of evolution.

Babies can't talk, so it's probably a way to communicate to the parents and illicit an instinctive response.

Eyes are important for survival, and also susceptible to debris and damage. Babies are inexperienced and explore and experiment with their surroundings in dumb ways. So if a baby is hurt or upset, it might make sense to flush the eyes out just in case. If an eye irritant is the reason the baby is upset, the cost of a few tears is very low compared to the value of the eyes.

A lot of animal behaviors emerged via evolution because they "just work" in certain situations in the wild. They don't always make a lot of sense to us today, sitting indoors in front of our screens. But they worked well enough for some scenarios to carry forward.

Non-verbal communication. It helps when you can't say you are hurt but your tribe can see you are crying, thus in distress and help.

Actually when we cry we release certain types of chemicals and endorphins which make us feel good. Kinda like your body is saying hey you're sad, this will cheer you up.

Mostly because I'm a failure at being a functional human being. Sometimes it's because I stubbed my toe, or I hit my funny bone. Usually it's the soul-crushing despair, though.

Are you a terminator?

https://m.youtube.com/watch?v=vwboVf4287E

So, catharsis aside, tears help keep your eyes from drying out, provide lubricant for your eyelids, and help remove debris while providing some protection of that debris scratching on the way out.

Quick search:

Crying is an important safety valve, largely because keeping difficult feelings inside — what psychologists call repressive coping — can be bad for our health. Studies have linked repressive coping with a less resilient immune system, cardiovascular disease, and hypertension, as well as with mental health conditions, including stress, anxiety, and depression. Crying has also been shown to increase attachment behavior, encouraging closeness, empathy, and support from friends and family.

Scientists divide the liquid product of crying into three distinct categories: reflex tears, continuous tears, and emotional tears. The first two categories perform the important function of removing debris such as smoke and dust from our eyes, and lubricating our eyes to help protect them from infection. Their content is 98% water.

It’s the third category, emotional tears (which flush stress hormones and other toxins out of our system), that potentially offers the most health benefits. Researchers have established that crying releases oxytocin and endogenous opioids, also known as endorphins. These feel-good chemicals help ease both physical and emotional pain. Popular culture, for its part, has always known the value of a good cry as a way to feel better — and maybe even to experience physical pleasure. The millions of people who watched classic tearjerker films such as West Side Story or Titanic (among others) will likely attest to that fact.

There are times when crying can be a sign of a problem, especially if it happens very frequently and/or for no apparent reason, or when crying starts to affect daily activities or becomes uncontrollable. Conversely, people suffering from certain kinds of clinical depression may actually not be able to cry, even when they feel like it. In any of these situations, it would be best to see a medical professional who can help diagnose the problem and suggest appropriate treatment.

https://www.health.harvard.edu/blog/is-crying-good-for-you-2021030122020

https://www.mindful.org/why-crying-equals-thriving/

https://www.psychologytoday.com/us/blog/talking-apes/201910/the-secret-reason-why-we-cry

https://www.youtube.com/watch?v=AdMNYn2MEac I know now why you cry. But it's something I can never do.

I heard that there are 3 types of tears, and the type that comes out when we're upset has a natural painkiller in them.

Based on empirical evidence, the last three times were: an abscess bursting in a sensitive area, being kicked in the nuts, and eating really good cheese. Pain, pain, delight.