I’ve kept journals. Diaries. Books of notes handed back and forth with friends. Social media chronicles on Twitter and Facebook. This blog.

Millions of people across the globe have journals in one form or another:

• They chronicle events. My great-grandmother’s diary recorded what she accomplished and what had happened over the course of the day.

• They document emotions and thoughts about happenings, from world events to personal-life moments and milestones. I peppered my adolescence and young adulthood with attempts at journals of the emotion-recording kind, though I never kept them going long.

• They hold people accountable to their goals through recording intentions and checking progress against plan. When I’ve needed especial focus to keep on track, I’ve maintained this type of journal.

• They affirm the goodness in our lives through prompting us to write down things for which we feel thankful. I’ve done this as well in pensive times.

Journals that made it through history’s wringer have helped historians better understand distant eras and places (noted in my post about Samuel Pepys). Information’s explosion in recent years means historians of the future will have a treasure trove for understanding our world. Already scientists and statisticians have developed tools to analyze texts and the Web for trends, including Google’s lauded Ngram Viewer.

Perhaps only journals and diaries handwritten on paper will stay safe from future analysis. But do we want that? Don’t most people write journals with some future audience in mind—even if only after they’ve left this mortal coil? Of the above journal categories, only the latter two types seem valuable solely for the moment in which the person writes them and as part of the therapy of writing, rather than for an end result to revisit in the future.

Do you journal? Why?