Balanced means it will enforce throttling and other power savings techniques to everything it can. Power savings settings can and are different between AC and DC states.
Some of the items that are affected by this.
The hard drive, Internet Explorer, slide show backgrounds are paused in balanced, the wireless nic, time until sleep on the system, usb suspension, the graphics card, NIC link state, CPU throttling min and max amounts, display brightness, multimedia playback, java, video quality, battery notifications and actions.