Making a bootable DEBIAN USB stick with Persistence

A lot of discussions exist here on making a bootable USB stick. Debian manual on installing Wheezy suggest the following:

# cp debian.iso /dev/sdX
# sync

Making sure the USB device is first unmounted.
Debian manual page.

A possibly better way of doing it is with dd. which does byte copy. the syntax would be

dd if=debian.iso of=/dev/sdX

and the command will need to be run as root. dd allows you to have more control if you want it. Check out it's man page here or Debian instructions on how to create a bootable USB stick here.
(Where sdX maybe the full name of the drive, with the number, for instance /dev/sdc1.)

It would probably be better to use an unmounted device because you are overwriting the entire partition structure that is formatted in say fat or ext3 or ntfs and replacing it with the cdrom or dvd format (usually UDF). If the operating system is writing to the filesystem while it gets overwritten it could be a bad thing. the block device /dev/sdx basically is a virtual file allowing binary access to the entire harddrive.

Make your usb persistent:
For example:

dd if=debian-live-8.6.0-amd64-cinnamon-desktop.iso of=/dev/sdx

unmount your USB then run Gparted , select your USB , right click on the unallocated partition and select new , create the new partition as follow :

Create as: Primary partition
File System: ext2 
label: live-rw

Apply changes and boot from USB with persistence .