This has puzzled me for far too long. Sometimes, a simple copy/paste of the contents of the iso is enough to make a bootable usb for the OS I try to use, while sometimes, copy paste does not work while other software like unetbootin work. I keep my usb drive in FAT32.
My question is why does this happen and why is it not reliable to just copy the iso's contents? In contrast, dd also always works.
In general it's always a good idea to have a fresh USB drive made bootable. If you simply copy and past, if for any reason a program had written files to the drive it could corrupt your install. Unless you are copying from a stock folder from your desktop.
I use Rufus to create my bootable USB drives. You can chose your format and the program will also format the USB drive for you to ensure a good, clean install. It also creates the files that your computer uses to recognize a bootable device.
Copy and past just leads to issues, it may work, but can break at any time.
