So why not just move the files to the actual HDD then? There is one, isn't there? Something about 3 TB for the price, right?
Most people have a single drive in their MacBook, and it is either an HDD or a SSD. One or the other. They aren't moving their files internally if they have only one drive. I recommend having an SSD as a boot drive, and using an external HDD. Have your essential files on the boot drive so they can easily go where you go. Not a big deal to also carry a small external HDD case around for the larger file storage. My daughter has a Macbook Air and complains her drive is full, yet ignores me when I tell her to simply move files to an external and carry it too. So be it.
I keep the majority of my files on external drives, and only the basic system stuff on the internal drive. That way, I have about external 12 TB always accessible and the internal SSD drive is fast and nimble. (6TB RAID array, and several 2TB or 3TB drives available externally). I don't like my stuff in the cloud not totally under my control. Desktop and tower machines are easier for having multiple internal drives, but a lot of people want portability.
Not if you don't need one. The vast majority of people don't need one.