You do not need to reformat the memory card after you transfer the photos. Just delete them. Formatting buys you nothing, in fact it has a down side. File recovery software will NOT work. When you delete a file, you remove it from the "FAT" (File Allocation Table). The FAT is an "address" book that has the location of every file on the card. The data (photo) is still out there. When you take a new photo, a new entry is made in the FAT and the old date is overwritten. You don't loose storage. A format overwrites EVERYTHING, FAT and old data. Your computer sees the card as a disc drive. Trust me, I know what I'm talking about. I worked on disc storage systems for the 44 years of my working life (the last 12 with EMC). I'm now retired.