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Sleep deprivation is a kind of torture – whether you suffer from insomnia, have just no time, or are improsioned (yes, they really use it as a kind of torture). The human body should re-fuel every 12 hours, among the reasons is that our brain clears toxic byproducts of neural activity while we sleep. But this process also takes place when we are deprived of sleep  but in the not so good way thus cleaning away valid and important neuronal connections, which will lead eventually to brain-damage.

Michele Bellesi and his team from the Marche Polytechnic University of Italy examined brains of mammals when they were put under pressure of poor sleeping quality.
The neurons in the brain are refreshed by two different types of glial cells, the microglial, which is responsible for a process called  phagotosis, cleaning out and devouring old and worn out cells and the astrocytes, which cuts unnecessary synapses. 

With sleep deprivation, the brain starts to literally eat itself; this was found out in an experiment where the researchers imaged the brains of four group of mice. One group slept six to eight hours, thus was well-rested; a second was periodically woken up; the third was kept awake for eight extra hours, and the final one was kept awake straight for five days.
The outcome showed that the astrocytes “ate” 5,7 percent of the synapses in the first group, but up to 7,3 percent in the second one; in group three this raised to 8,4 and it the fourth group to 13,5.
The microglial cells showed similar statements.
This outcome suggests a connection between lack of sleep and neurodegenerative diseases.