Power raking, dethatching and lawn combing are all the same thing, and designed to remove thatch. If you fertilize regularly or leave heavy clippings on your lawn, consider dethatching. After thatch is pulled it must be collected or you defeat the purpose entirely. Understand that thatch is a buildup of roots, crowns, twigs, seeds, clippings and old leaf matter that cannot decompose at healthy rates.  Thatch buildup is basically a form of lawn dandruff. Over time it requires a good scrubbing and this is  where power raking comes in.  Please note some thatch is good. It regulates soil temperatures, keeps crowns cool when heat increases, retains moisture and some nutrients. But, when thatch reaches a layer more than 1/2 an inch problems can occur. Essential nutrients and air must leach their way through a dense layer of decaying material. This delays a lawns ability to eat healthy meals. Lawns gradually become supressed, and over time pests call your lawn home. As stress compiles, the lawns ability to fight will soon come to an end. All vibrancy and vigor is lost from a slow process of suffocation, suppression, infestation and death. 
The home owner is responsible to pick up all toys, cords, and mark all buried items like sprinkler heads...etc, this avoids contact with the equipment's reals. Power rakes can be very unforgiving when used improperly, so be cautious if you are inexperienced.... DO NOT dethatch when temps are high or lawns are dry from heat. You can damage the grass crowns severely by scalping weak areas. Upon completion of power raking and thatch cleanup , apply fertilizer and then water. The safest time to dethatch is mid May - end of June and fall...it really depends on weather and the lawns condition.

Power Raking

Core aeration is probably the best lawn service any home owner should consider. It is usually done once per year but two is optimal. This service can be done throughout the lawn season. (Some people say its better to aerate in the spring or fall. I think if your lawn is compacted and requires aerating...why wait. Give it care now before it gets worse. That's the same as saying; the best time to seek medical attention is in the spring or fall...that logic makes no sense).

Its better to aerate when lawns are moist so tines get better penetration. Core aeration removes thousands of soil plugs from a lawn and provides so many benefits. It alleviates soil compaction, allows oxygen-water-nitrates-phosphates-potassium and other elements to reach the root zone quickly. Other benefits are; lawns are lusher, deeper roots, less watering, more drought resistance and standing water puddles are lowered.  It is also a form of dethatching which brings microorganisms to the surface aiding in thatch breakdown, and a mild top-dressing. It also provides an opportunity for over-seeding because there's better seed to soil contact from plug holes.  Always leave the aeration plugs on the lawn, it may look unsightly but its better to leave them on. In the end this equates to a thicker healthier lawn, helping to choke out weeds and lower disease. 
If you choose  to aerate, the homeowner is responsible to mark all sprinkler  heads or other concealed items prior to aeration. This avoids equipment contacting them. Fertilize immediately after so the granules enter the plug holes...then water in.
Do not aerate a newly seeded lawn until it has reached full maturity and the soil is firm. This may take 1-2 growing seasons (approx. 100 growing days in Saskatchewan, Canada per year). Aerating to early may lift your new sod up. Check your sod by grabbing it like a head of hair. Jerk it around and feel for any shifting or try lifting up an edge. If there's any movement or doubts do not aerate, recheck at a later date.

Core Aeration