Sort of, it is for the untrained driver that doesn't anticipate the road ahead, i.e, those that are either on the gas or brakes all the time, since they spend a LOT of gas accelerating all that mass. The mass is an energy storage device though, once you learn momentum management and to anticipate stops and traffic patterns, much of the benefit goes away. On a steady highway drive it only has any bearing on FE in the 10 seconds you get to highway speed, in the city it's that 10 seconds slow acceleration at every stop light, so in city driving it counts more.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
Probably the easiest way to get more MPG is to inflate your tires beyond your car manufacturer's recommendation but not beyond the tire's rated maximum (check the link in my sig about tire pressure). Remove any unnecessary external accessories such as antennas and racks.
It's the easiest, but it's not very effective. The most effective way is to alter your driving habits. You can read all about that in the various discussions here, or review an introduction article such as the one linked in my sig.