Before you start either section of your lab exam (Troubleshooting or Configuration), your proctor is going to remind you to save your configurations often. You might even see this written several times in the lab instructions contained in the new GUI. Why are you being asked to do this?
Well, at the very least, you might have a device that hits a snag and just decides to reboot on you. How rude! It is never fun to lose any amount of configuration when you are pressed for time, as you will be in the certification lab exam. But in the worst case scenario, your entire rack of equipment might power cycle due to a catastrophic failure in the Cisco facility that houses your equipment (real and emulated equipment). This could amount to you failing the exam for sure if you were not consistently saving configurations as you go along.
Here was the habit I developed for saving my configurations as I went along. After making a configuration on a local device and performing whatever necessary verifications, I would then type wr or do wrdepending on the configuration mode. Then, while the device is performing its save, I would leave for my next device in the configuration. Using this method, I was completely confident that everything was always tucked away nicely in the startup configuration and did not fear the unplanned reboot.
Whatever your method of saving configurations will be - be sure you practice, practice, practice it prior to sitting your actual lab.
P.S. The only issue I ever had with my approach was that in production networks, I would often find myself compulsively saving configurations, even when I did not want to. :-(