what is the difference between providing 7 volts or 12 volts to arduino uno? according to this the recommended input voltage is between 7 and 12 volts.
The question is what is the difference between providing 7 volts(minimum recommended volts) and 12 volts(maximum recommended volts) ?.
The amount of heat dissipated by the voltage regulator.  The higher the voltage you supply the hotter the regulator will get.