The address details pane is a rather recent addition to IDA so probably not many users are familiar with it yet. However, it can be a quite useful addition to the standard workflow, permitting you to perform some common tasks faster.
Address details view
On invoking View > Open subview > Address details (you can also use the Quick view selector), a new pane appears, by default on the right side of the main window. Obviously, it can be moved and docked elsewhere if you prefer. It will automatically update itself using the current address in any address-based view (IDA View, Hex View, Pseudocode).
The pane consists of three sections, each of which can be collapsed and expanded using the triangle icon in the top left corner.
This is basically a non-modal version of the standard Rename address dialog (N hotkey). It allows you to quickly rename locations by entering a new name in the edit box as well as view and change various name attributes.
This is an expanded version of the Print internal flags action, however currently it does not provide details of instruction operands.
Data inspector section
This section shows how the bytes at the current address can be interpreted in various formats: integers, floating-point values, or string literals. It can be especially useful when exploring unknown file formats or arrays of unknown data in programs.