Cats may hide behind their litterbox if they don't have any other options.
Results supported that the hiding box decreased stress in the group of cats that had them. By days three and four, their CSS scores were significantly lower than the control group (note: by fourteen days, both groups of cats had similar stress scores). The findings also demonstrated a strong need for a hiding space. The cats with a hiding box spent 55% of their time in the box. Cats without a hiding box spent almost as much time (45% of observations) lying behind their litterbox, suggesting that cats deprived of an appropriate hiding space will make the best use they can of available materials to find a place to hide (even if it's not a very good place). The findings also demonstrated that it wasn't enough to have bedding (previous research showed that cats prefer a towel as a substrate to lie on). The cats really wanted to be IN that box!
Now earlier on, I said that boxes may save lives. How?
Cats, even ones that were loving, well-adjusted pets a day ago, often experience extreme levels of stress and fear in new environments. This behavior has some evolutionary origins (as predators AND prey, cats are vulnerable in unfamiliar situations) as well as some human-caused ones, such as lack of early socialization. Many pet cats rarely leave their home, and may not have been exposed to strange people, other animals, or the types of handling encountered upon impound in a shelter (such as medical examination).