I found this question interesting because I had some exposure to large factory power-conditioning units almost ten years ago early in my career. These units were the size of small cars and could provide power backup to the electronics running the machines and power conditioning to entire factories with endless assembly lines.
The concept is not simple. However, you can imagine that a factory has a large electrical supply to run all of its equipment. This supply of power from the local electric company is much different than the 100-200 Amp service coming into your home. The one similarity is that both power lines supply electricity in a raw and "noisy" way. I use the term "noise" because of the science involved; however, it can be just as easy to think of it as "dirty." The power conditioner has the ability to "clean up" the noise in the electrical supply, which can be beneficial to equipment that transfers electrical energy into mechanical energy and requires inductive or non-linear loads (electrical motors and compressors, pumps, AC units, etc.).
The major difference with these types of equipment when compared to lights, computers and microwaves, for example, is that their strain on the supply system is not reflected on the meter reading. Our homes have equipment that produces the same reactive loads in the form of refrigerators, AC compressors, Jacuzzi and pool motors, etc. However, these loads are not significant enough for the electrical utility company to charge us for them. On the other hand, manufacturing plants and industrial facilities are charged a fee to compensate for the loss of power on the supply side as a result of running their machines.
While I believe this science is evolving, there is currently no data to believe that a power-conditioning unit can provide efficiency or cost savings. The Energy Star website also addresses parts of this question here.
Lastly, having worked on projects that involve automation, power monitoring, and renewable energy, it is still a great idea if you are incorporating any/all of these components in your home to install a whole-house surge protector. The cost to buy and install one of these as part of a new construction or renovation project is a great insurance policy for some of the hard-wired electronics involved in those systems.
Best of luck on your project!