You tell yourself that you need everything on it, but you know it's not true. You used to treat your Mac like gold, but these days it's old, slow and full. The cold hard truth is that you got sloppy.
Your computer has reached the end of its limits and you don't have the cash to drop on a new one. An unwelcome window that popped up out of no where to inform you that your startup disk is full. Your startup disk is almost full, now what?