Thanks, fattie! I write web apps (SPA) and I use localStorage a lot to store "user preferences," typically things that involve presentation only like a modal's size and position or a "Do not show this confirmation prompt again" flag. The user expects these preferences to be preserved between sessions so localStorage is perfect. They would also expect these preferences to be shared when they open a second tab for the same app. On the other hand, sometimes I pass data between pages using localStorage. Seems like I need to shift these to session storage because they only confuse things if they affect both tabs. I need to go back and evaluate each and every case, to give the user the best multi-tab experience.

BTW, why do I use localStorage instead of using the app's back end server? Mostly because the back end is developed by a separate team and I don't like to bother them for features that only effect the web UI. Well, really, because they don't like to be bothered! (Understandable. They've already got plenty on their plate.)