For full body zentai suits, zipper is an necessary accessory. As the best way to seal the costumes and burden the possible shrink or stretch, most zipper's located vertically at back of the suit, and length's from head to end of back. This zipper allows you to go in and out of the suit easily, and get you fully encased.
Except this very basic long zipper, we could add other zippers into the suit for other functions, or for personal preference. The most practical zipper should be the crotch zipper, which saves us the trouble when we are in a suit. For easiness of enjoying the zentai outfit, many people select a suit with removable hood, and if the hood could be connected with the suit by a hidden zipper, it will be easy to take on and off. Other than these two, for better visual sights, some people would order suit with the eye holes, but this means it can't be full body zentai suits, so use two short zippers for eyes seem a better choice. Also, if you want to enjoy some drinks while in your comfortable zentai costume, a mouth zipper could help a lot.
Some zentai suits are used for performance, or for game play. For some magical effects, the gloves and socks could be connected with zippers, and put off to show the inside. Some people love to have chest and belly zippers, located horizontal at front. Sometimes people wear two or three layers of zentai suits, and take off the first one or two layers, could make the cool combination of "black body" and "white hands and legs".
Right now most zippers are delicate tailored onto the zentai costume, and hidden well. Unless it's revealed for some purposes, it's hard to see how many zippers one zentai suit has, and where they are located.