Skin tight suits that cover the entire body are commonly called zentai (from the Japanese ゼンタイ). This is possibly a contraction of zenshin taitsu (全身タイツ) or "full-body tights". Zentai is most commonly made using nylon/spandex blends, but other materials such as cotton and wool are used as well.
Such suits are used in the arts to diminish the presence of an actor in a scene. In fact, in the traditional Japanese art of puppetry called bunraku the apprentice performers are completely covered in black garments against a black background to produce the same effect. Zentai is also used by artists as a medium to accentuate the body, sometimes making use of vibrant patterns. By making the performer anonymous, the performance of the body itself becomes the focus. Flesh tone cotton suits are often used by cosplayers in Japan to provide a base layer that looks like the cel-shaded skin of the animated character.
Practical uses aside, zentai is most often associated with spandex fetishism. Indeed, zentai fechi (ゼンタイフェチ) literally means "zentai fetish". Some zentai fetishists are after the experience of total enclosure, while for others it provides a way to anonymously enjoy exhibitionism. One might also experience it as a form of sexual bondage, even though it does not restrict the motion of the body or even act as an effective blindfold.
However, there are some who enjoy zentai for the sensory novelty or physical comfort without any sexual connotations. People with autism can find it calming to wear spandex garments. Some even find it useful as an aid for meditation. It can provide a medium for body awareness, a focus for mediatation via the senses, or a symbolic barrier between the self and the world.