What are advantages/disadvantages of Habilitation over PostDoc in case of academic career? As far as I know a PostDoc in USA is 2 years of research program. Habilitation is 4-8 years program. So, why is this difference in time frame?

What are advantages/disadvantages of Habilitation over PostDoc in case of academic career?
PosDocs usually work on someone else's research programs. Often the program is an incremental or partial step in a larger research framework. Postdocs have some independence in choosing the methods for their research, but are largely supervised/trained by their PIs or mentors. Postdoctoral projects can be rather technical in nature. They usually result in a few journal publications. It is very likely that your colleague next door did or will do a few postdoctoral projects during their career. 

Habilitation is a large piece of work focused on a large problem, performed completely independently by one person. It usually contains major theoretical breakthrough (e.g. a completely new methodology) and results in a number of journal publication and at least one major "manuscript" publication (e.g. book). It is not so likely that a random academic next door did a Habilitation (because in most countries PhD is a terminal degree and Hab. does not exist).

tl;dr: Postocs and Habilitation are completely different programs.