sources.list:ordre de préférence

salut à tous et toutes

faut il un ordre de préférence dans le sources.list?

le mien :

###DEBIAN STABLE & BACKPORTS

#Debian-jessie
deb [url]http://ift.tt/1JzP15r] jessie main contrib non-free
#deb-src [url]http://ift.tt/1JzP15r] jessie main non-free contrib

#Debian-jessie-security
deb [url]http://ift.tt/vA9OyK] jessie/updates main contrib non-free
#deb-src [url]http://ift.tt/vA9OyK] jessie/updates main contrib non-free

#Debian-jessie-updates, previously known as 'volatile'
deb [url]http://ift.tt/1JzP15r] jessie-updates main contrib non-free
#deb-src [url]http://ift.tt/1JzP15r] jessie-updates main contrib non-free

#Debian-jessie-backports
deb [url]http://ift.tt/1JzP15r] jessie-backports main contrib non-free
#deb-src [url]http://ift.tt/1JzOZKT] jessie-backports main contrib non-free

#Debian-jessie-iceweasel-release
#deb [url]http://ift.tt/1PaXd2W] jessie-backports iceweasel-release

sources.list:ordre de préférence