Refer to figure.
The total mass of the helicopter can be said to act through one point called Centre of Gravity (CG).

An aft CG results in a nose-up fuselage attitude, will reduce drag, the stabiliser will be less loaded, thus the range, endurance and rate of climb capability will increase, and its fuel consumption will decrease.

Also, the nose-up fuselage attitude will make flare manoeuvre easier, since there will be more aft cyclic range available.

However, with aft CG, the forward cyclic required for high speed thrust is more, increasing the bending moment on the rotor mast.

If the CG is too far aft, behind the aft limit, there may be insufficient forward cyclic to prevent the tail rotor and boom from striking the ground. Wind is also a factor, because blowback requires forward cyclic and this may already be at its forward limit.