Refer to figure.
CG position VS Aircraft’s performance
A tail down force (created by the elevator) exists to balance the moment created between the CG and CP of the wing. Essentially, the tail works as an upside down wing which generates lift downwards. The amount of lift it needs to generate will depend on CG position and aircraft weight. Consequently, when the CG moves forward and aft, tail down force and lift required for a stable flight will change.

• FORWARD CG increases the pitch down moment tendency of the aircraft. Therefore, greater horizontal stabilizer and elevator deflections are needed to give the aircraft a pitch-up attitude to compensate for the pitch-down moment. Extra lift is generated by increasing the angle of attack, which in turn increases induced drag. Thus performance decreases.
  For take-off, if the CG position is too far forward, the aircraft is said to have a “heavy nose”.
• Conversely, as the CG MOVES REARWARD, the aircraft will experience a reduced pitch down moment tendency, resulting in less tail-down force being required. As a consequence, drag decreases (and so does stalling speed) which improves performance. Since Climb gradient is a product of excess of thrust over drag, climb performance will be improved.
  For take-off, if the CG position is too far aft, the aircraft is said to have a “light nose” making the rotation easier. Additionally, an aircraft which requires less lift will have a slower rotation speed, which results in a reduced take-off distance.

To simplify this concept and make it easier to answer these type of question you can think of a forward CG as having the same effects as a heavy aircraft; and an aft CG as having the same result as a light aircraft.