The conserve attribute essentially is a multiplier on the particle's velocity. For example, if a particle has velocity 100 at frame 1 and a conserve of 0.5, then a frame 2 the velocity would be 50, at frame 3 it would be 25, and so on.
So, the conserve attribute acts as a brake on the velocity.
In the physical world, mass (specifically Inertial mass) can be defined as 'resistance to acceleration'. When simulating particle dynamics we can use mass as a dampening effect on the motion of a particle, in a similar way that conserve does. The main difference is that we can define the mass on a per-particle basis: the higher the mass the higher the resistance to motion and the lower the 'conservePP' value we are creating.