Planetary Nebula (PN) shells and AGB circumstellar envelopes evolve under a wide range of external conditions, from the high ISM densities found in the Galactic plane, to the rarefied and hot intracluster medium where the systemic velocity of the star can be as high as 2000 km s-1. We explore the effects that the external pressure and/or stellar systemic velocity have on the observable properties of PNe. We investigate how the mass and size of the PN halos are reduced when the star is moving with respect to the external medium. We have studied as well how the mass of the circumstellar envelope is fed by ISM material when high ISM densities characteristic of the Galactic plane are considered. By studying the evolution of PNe in the intracluster medium in Virgo, we infer shorter PN lifetimes than what is usually adopted. This has important implications, since the assumed PN lifetime strongly affects the fraction of intracluster light derived from PN studies.