Sleep is obviously very important to overall mood, anxiety and mental health. I personally need around seven and a half hours of sleep every night on a regular basis to feel good. I can get away with a bit less if I nap in the afternoon, and can go a few days with a bit less and catch up, but being chronically sleep deprived - with an outstanding “sleep debt” (not sure if that concept has been discredited?) - is very unpleasant.
There is a very distinct physical feeling when you haven’t slept enough. It’s a type of inertia, pulling you towards the sleep you have missed. It is obviously required for us to live, must serve some evolutionary purpose, and we are not designed to go without it. Much like food and water. Personally I get very irritable, forgetful and unfocussed if I haven’t had enough sleep.
Parenting handed me my longest periods of sleep deprivation. Infants have very different sleep requirements than adults - newborns don’t really have a concept of day and night at first, and just eat and sleep on a continuous cycle until they begin to build circadian rythyms and ultimately sleep more hours at night and fewer during the day. This means the sleep of parents of newborns is broken, sleep hours and quality reduced dramatically. It gets better, but there can always be periods of “regression” where it’s bad again, when some period of intense growth or change messes with the sleep patterns.
Of course many people search for “solutions” to this problem, to force the baby to fit into the parents' sleep schedule. “It’s better if everyone sleeps well”, goes the justification, and lots people are OK with the “cry it out method”, which feels to me a little much for a very small baby - maybe once they’re a bit over a year old and starting to communicate then there is the potential to know which outbursts are genuine emotion, that should be acknowledged and addressed appropriately, or just frustration in not getting their way, which should also be acknowledged, but not indulged necessarily. Early on when the parents (and the child!) are still learning how the child communicates, I wouldn’t have always been able to make this distinction, and cry it out felt too much.
The industry of sleep counsellors or sleep therapists for babies is growing and growing; I have been advised by many many people to hire one to help with our sleep problems. Do we actually have a sleep problem though? Or is just a direct consequence of our decision to literally make a new human being. Society is to blame here I suppose, we’re all to blame, for the insane grind culture that we’ve whipped ourselves up into. There’s no flexibility for the parents after the child is born - back to work after two weeks if you’re the father, six months if you’re the mother - so there’s no choice but to force the child to adapt to the parents' sleep schedules so everyone can remain sane.