Why Do I Need To Eject USB Drives Before Removing them?

We have been using USB drive  for a long time now. These have been very user friendly and  fast unlike other storage devices like CD or DVD drives.
When you enter the USB device, you can see  USB indicator icon towards the right side in the system tray and automatically the drive will open with pop up window. You can see all your files stored there or you can copy and paste file from computer. After right clicking and using eject button USB drive indicator icon with message will display "Safely Remove Hardware". Now why this message is shown and why not can we simply remove USB device.

Why Use Eject Button

The answer is that most operating systems use write cache that is good for better performance and unsafe removing of device  can result in loss and corruption of data. When you try to eject device by using stop or eject button, OS will remove all cache, check if all actions are performed and any USB drive file is open or not. After checking it will give message for safe removal of USB device with indicating message appearing. If any file is open or in use OS cannot flush out all the cache. It will give message "The Device is ...  again later" accordingly for different OS.

 The warning message ensures that pending tasks or write cache does not remain before final ejection of device. There may be other possibility that file is still locked, not open and still message is displayed. There may be some reason unknown why OS is not able to flush all cache and drive is not free from OS. For this you can use unlocker utility to unlock the program, file and is also used for deleting and sharing violation. You can also use Pro-Eject utility that detects all drives, removes Windows Registry entry, recent entries and closes any open applications,  files.

In long run its always recommended to use stop or eject button  to safely remove hardware device. OS  system is very less likely to face any problem of any data loss or corruption and error reporting message.