To reset all RAM and hardware registers to a zero or blank condition. Selecting Restart to reboot the computer does not clear memory, but turning it off and on again guarantees that memory is cleared and the system is reset. With laptops and home entertainment equipment, even that is not sufficient (see cold boot
A Remedy for Many Problems
Rebooting is the first action users should take when any computer, smartphone, tablet, router or other electronics device stops working, slows down or acts erratic. No matter how small the product these days, there may be a CPU inside with values stored and updated in memory as the device is used.