SSD is just like thumbdrives. You can move them around while using. The danger of moving HDD while running is because they have physical platters spinning with reading arms hovering above it at very close range (few microns). So if the platters were moved while they're spinning, the arms could scratch the platters. You can also cause the arms to move to another region while it is writing/reading, causing it to write/read wrong information and damage the HDD.