Writing summaries is not only useful before exams. Consider summaries as a communication means between you and your future self. Compression is a means to an end. Summarize to ease understanding, not just to reduce the word count.
Progressive summarization is the process of progressively summarizing information as you consume or review it. Doing so will be a great opportunity to dig deeper, think further, and add new notes to your knowledge base.
As an example, if you’re done taking notes for a book and have created a number of literature notes and permanent notes as a result, then you can review those and summarize the information.
Progressive summarization is useful because it makes information more approachable over time. If you have a hundred pages worth of notes about a book, then you have probably captured all the relevant information it contained. But that is a lot. A **few months from now, those notes will feel alien to you. What your future self will need is a summary to accompany those notes. That summary will allow your future self to quickly evaluate whether those notes are going to be useful or not for the problems at hand.
Summaries make it much easier to review and digest existing notes. Progressive summarization is thus all about compressing information to make it easier to (re-)understand and evaluate.
In a sense, progressive summarization aims to facilitate communication between you and your future self.