We cannot deny that it is important to always backup your data. It is even much more important to backup your entire Raspberry Pi SD card after going thru so much to setting up all the configuration which you never want to go thru again.
Therefore you should create a img of the SD card by doing the below on either a Linux or Mac machine
sudo dd bs=1M if=/dev/sdb of=raspbian.img
To restore from the img, simply do the below
sudo dd bs=1M if=raspbian.img of=/dev/sdb
While the Raspberry Pi Foundation recommend us to use bs=4M, it does not seem to work for me and hence I had decided to go with bs=1M even though it might be a lot slower but it works.
Just to note, if you are running Raspbian Jessie on Raspberry Pi 2, using the exact same SD card or img on a Raspberry Pi 3 is perfectly fine. There is no need for further configuration and it works out of the box. The only thing is that you might want to do a “sudo apt-get update” to fetch some of the specific updates for Raspberry Pi 3 hardware.