Fuel Pump efficiency and life span

Only possible if the tank is above the pump, if not, then the pump has to work to get the fuel - terms like positive head and suction head are used.

Does the weight of petrol in your tank help Pump to work better by pushing against/through pump so the Pump not having to pump so hard the Petrol?

In order to understand this, you need to understand how hydrostatic pressure operates.

Any liquid has a hydrostatic pressure calculated from its surface. The pressure is its density multiplied by gravity multiplied by the height difference from its surface.

Example:

You have gasoline fuel (750 kg/m³), on earth (9.81 m/s²), and your tank is 0.3 meters deep and full of gasoline. The hydrostatic pressure at its bottom is 750*9.81*0.3 = 2207 Pa. As 1 bar is 100 000 Pa, in other words it is 0.02 bar. Quite negligible, and in fact nothing compared to something like 10 bar pressure in low-pressure fuel injection systems.

If your fuel injectors are above the surface of the gasoline in the tank (very likely), for example 0.7 meters above it, then you have pressure 750*9.81*(-0.7) = -5150 Pa = -0.05 bar. As the pressure is negative, the fuel doesn't naturally flow and a pump has to provide the pressure.

The fuel pump has to provide this pressure and also the far greater pressure that is present in the injection system.

However, if your tank is nearly empty having only 10 cm of gasoline in it, then the height difference between the injectors and surface of gasoline is 0.9 meters and the pressure is then -6620 Pa = about -0.066 bar.

So, yes, the more fuel you have in the tank, the easier time the fuel pump has to raise the fuel to the level of the injectors. However, all of this is practically nothing compared to the pressures the fuel pump has to anyway provide, so in practice we can safely say: the effect is negligible.