What is PageRank sculpting?
PageRank sculpting is a technique used to optimize the flow of a website's popularity stream.
The overall picture is to maximize available popularity in order to send as much energy as possible to strategically well ranked pages and as little energy as possible to less important pages.
The impact of this process can be huge on major websites, with an architecture that is poorly optimized for SEO and enjoys quite a popularity.
Many SEOs have used PageRank sculpting through the attribute rel="nofollow" in the past. Aware of the misappropriation of this attribute, Google ended up rendering this type of optimization obsolete.
Efficient? As long as the internal linking will play a key role in search engines algorithms, it obviously will remain efficient.