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Your camera's memory card is a critical component in the data chain that connects capture to output. Lightroom has a very respectful approach to working with your memory card; however, it is up to you to use it to its fullest.
By only offering copy options from your memory card to your hard disk, Lightroom ensures that it does not alter the data on the card itself. This way, if something should go wrong during the copy process your original data on the card is safe. Furthermore, Lightroom provides an option to create a backup copy of your memory card, which means it can copy the data on your memory card to two places at once! This can provide great piece of mind that your capture data is safe before you format that memory card.
I do get asked from time to time about why can't Lightroom format the memory card after import. Well the reason is that A) you should verify that the data is safe before you format, and B) the best place to format your card is in the camera that will use it. By formatting in camera you are ensuring that the disk is formatted in the way that is best for that camera, which reduces the chances of data corruption during use.