Upside - nothing survives if done correctly
1. you get back all the junk that was pre installed and loose everything you have installed since.
2. The image is usually on a hidden partition on the hard drive, if the Hard drive fails you loose everything, sometime you cannot access the inbuilt tools for a startup repair or factory restore.
Buy something like Acronis True Image ad make a image on to an extrenal disk on a regular basis - you can restore to the same drive - or put in a bigger drive. and be back to normal without loosing anything in approx 15 minutes.