Today, nearly all production involves the recording of digital files. These files are the stored on some form of memory device.
As the production world moves from standard definition to high definition to even higher quality formats (like 4K) the amount of storage needed to hold the files gets larger.
Similarly, large video files need to be transferred rapidly. This means that specialized superfast storage devices sometimes need to be used for production.
Some cameras can record on off-the-shelf memory cards. But as the image quality increases, it becomes necessary to use faster storage media—which can sometimes be 100 times as expensive.