Computers are not 100% reliable, they break down, their performance is reduced by the addition of new software, they contract viruses, and sometimes they're just downright finicky. Sometimes their users accidentally cause minor glitches while experimenting with unknown file types or just may not be aware of the damage that deleting certain files can do to the systems. Companies hire full-time staff just to maintain the computers and networks their employees use, and this can be a very expensive proposition.