Because tablets have LCD screens, they do not need or use screensavers. Only old CRT monitors benefit from screensavers, due to the way they work. Moreover, screensavers are actually detrimental a tablet.
CRT displays tend to burn in images that are displayed for prolonged amounts of time. For instance, a CRT monitor connected to a Windows computer may burn in the taskbar at the bottom of the screen. CRT displays have phosphors that emit light to project images on the screen. When an area of the display projects the same image for a long time, the image causes some areas to remain darker. To prevent screen burn-in, operating systems display animated images when a screen remains still for a certain amount of time.
However, as LCD screens have no phosphors that project images, they do not need counter measures against burn-ins. As such, modern displays do not only make screensavers obsolete, but also render them wasteful. When a screen displays a screensaver instead of turning off, it only wastes electricity. Some screensavers even make the computer calculate complex 3-D images, increasing the energy requirement.
As all tablets use LCD screens and are not always plugged in to a power source, they do not use screensavers. If they did, they would run out of battery without actually saving the screen. When unused for a certain amount of time, tablets turn off the screen instead.