The problem with the idea is the difference in interface speeds and media-limited transfer rates. USB flash drives, in my experience, pass data on a USB interface at about 20 megabytes per second. That puts you squarely into the mid nineties in terms of disk performance (remember SCSI Fast 20?). The interface speed of internal SATA hard drives are much faster and the media transfer rate off the disk is typically 100 megabytes per second depending on the characteristics of the files being transferred.

That being said, at work I have a 16GB USB stick plugged into my machine that holds accumulated reference material that I rarely use but don't want to save on enterprise disk at $600 per TB or some other horrible waste of society's resources.

I confess, I have NO idea about transfer rates and other important items. That's why I turn to this chorus of experts. It seemed like a good idea, and I assumed that "flash drive" was the same as SSD, but now that I think about it, I realize it was not SO smart, in reality.