I spent several hours this weekend wrestling with a rented Bluebird Aerator.
I did about an acre of lawn. The machine is not as effective as the kind you tow, but it produces pretty good cores as long as the soil is not too dry and hard. Some heavily-used areas seemed to want to be done twice and some needed to be done thrice where most of the walking and wheelbarrowing is done, but I ran out of steam. It is said that the cores should be every 6 inches or so, but that is difficult to accomplish. The wrestling is because it's a heavy and top-heavy machine, tricky on slopes, and tough to turn without tearing your turf to shreds. After the plugging, I fertilized it all and overseeded the patchy spots. The results should be evident in early May.
Soil gets compressed by foot traffic, lawn mowing, wheelbarrows, etc. You can put a lawn on life support with extensive fertilization and irrigation, but it won't be healthy. Lawns that are walked on should be aerated each year, late Spring or Fall. Athletic fields are typically aerated twice a year and top-dressed once a year with a very thin layer of topsoil/sand mix.
Earthworms are excellent aerators too, but they won't live in compressed soil.