Today’s Question: Why does it matter if I remove a photo storage card without ejecting it from my iMac and get this “Disk Not Ejected Properly” message?
Tim’s Quick Answer: The reality is that as long as data is not being written to the media card (or other storage device) there is virtually no risk of harm. That said, I do recommend playing it safe and using the option to safely remove storage media before disconnecting it from your computer.
More Detail: The risk involved with not ejecting or safely removing is that files (or the entire storage device) could become corrupted. This is really only an issue if data is actually being written to the storage device. If you disconnect a storage device while data is being written, the data will be written incompletely, and one or more files may be corrupted.
When you are downloading photos from a media card to your computer, data is being read from the card but not written to the card. Therefore, there isn’t any risk of corruption to the card since no data is being written to the card. In other words, no change is actually being made to the card itself.
That said, I do recommend using the option to eject or safely remove the media card using the applicable feature in your computer’s operating system. I simply consider this a good habit to be in, as it can help ensure you don’t ever disconnect a storage device while data is actually being written to it, even though that isn’t a concern when simply downloading photos from a media card.
Note, by the way, that in the Import dialog in Lightroom Classic there is a checkbox you can turn on that will cause the card to be safely removed automatically when the import is complete, so you don’t need to take the extra step of using the operating system feature when downloading photos.