Linux halts the CPU in the idle cycle to further reduce power consumption. Early reports of OS/2, Win3.1/95, NT, and Linux showed Linux to use far less power than DOS-based O/S's that spun in the idle loop and consumed power -- this may have changed hence it would need research to validate.
Most Linux-users tend to leave their computer on for years whenever possible. However, several modern BIOS's support an unattended powerup, and with cron you can even do an unattended shutdown. No need to leave the computer on night after night.