It seems that the topic of sleeping, or system hybernating, does not concern server installations and a serious administrator can omit it. However, the serious administrator certainly has their own work station and it is often a laptop, naturally with the installed Linux therefore the knowledge about putting the system to sleep will be very useful. As for the server environments – currently it is popular to limit the use of energy by server sub-systems. On big server farms the limit of used power by 10% is calculated to hard cash from savings which the administrator can (and even should) get a bonus from. This is exactly the subject that ACPI deals with.