This window is similar to the "Cannot stop the device" window, except it displays a list of processes locking "neighbours" of the given device on a USB hub (not processes locking the given device itself).
Why is this necessary?
On returning a device back to the system, the program restarts not the given device, but the USB hub where that device is connected. If there are other devices connected to the hub as well as the device you wish to return, and if a process has files open on one of those neighbour devices, the hub will not allow itself to restart.
USB Safely Remove displays all processes have files open on "neighbour" devices and lets you close those processes or their files - thus enabling you to return the device back to the system successfully.
Since the "Cannot return the device" window and its controls perform similar functions to the "Cannot stop the device" window, please see the "Cannot stop the device" window description for further details.