Chrome Developer Tools -> Application -> Local Storage -> http://localhost
There are some key/value items in this panel and an extra Preview panel below.
The content of the Preview panel is the value of the above selected item, which is already visible above.
So what is the purpose of the Preview panel and how to remove it?
The thing is that a key can have multiple data points or long value, which for you to see you have to copy it and paste it in notepad or something to fully see what the value is. The preview panel helps because you can see multiple data points at the same time. You can't necessarily remove the panel(it's permanent), but you can hide it by dragging it downwards.
Reminder: This question was quite redundant. You could easily have guessed what the preview panel does with some research.