I found some articles, such as this article from SuperMemo and this article from Wikipedia, about incremental reading. I read quite often, and for many different purposes, but cannot understand in what situation one would need to use incremental reading. What is an example of a situation in which this method, considering the time investment needed, would be practical or necessary?
If you read the article on incremental reading on the SuperMemo website, it explains incrementally as more of a reading management method. Basically, humans are very bad at objectively determining the immediate value of anything they're considering, so it is easy to get in overinflated sense of value when reading any book, article, etc. incremental reading allows you to select interesting or possibly useful pieces of written information, and forces you to review them again in the future. Some information that seems important right away might not seem important weeks, months, or years later.
The other thing that incremental reading allows you to do is delay reading information if time, attention, or lack of understanding core concepts is achieved.
Imagine you decide to begin incrementally reading about the history of African government. You find a few pieces of interesting information, but nothing seems to grab your attention. You can choose to continue reading the article a few weeks or months later, when the information might be more relevant in your life. Basically, as you read anything, you have to constantly ask yourself "how important is this information in my life? How much is this worth learning?" Some information requires diligent study, others need to be glossed over quickly. Most written material contains a mixture of important and unimportant information, SuperMemo helps you to grab the pieces of information that are useful and consider them further.
In order for incremental reading to work, it requires the use of spaced repetition, something that has been playing it by SuperMemo for years. I don't work for them, but I am an enthusiastic users and I have been incrementally reading for at least 1 to 2 years, and I have been using SuperMemo for 8 to 9 years.