They might make you feel sick.
Everything has its own advantages and disadvantages including 3Dscreensavers. The major disadvantage of the 3D screen savers is the amount of system resources they require. If someone applies a heavy 3D screen saver on his computer then it could slow the whole system and make other programme work at a reduced speed in comparison to normally. One other big disadvantage is the processor heats up too much which in turn decreases the life of the processor.