How to use OBD2 memory saver ultimate guide

Testing an OBD II memory saver device on the 2002 Ford Crown Victoria P71 and the 2000 BMW 740 iL (e38). What are the advantages of using this device? What are the limitations? What can you use to power the device? Do you need one or can you find a work around?
I'll give a complete "every mans guide" to this device and answer any questions you may have had before watching this video.

[@cqmacht4513]

Whenever you use a memory saver hook it up and close all doors do not turn on anything ,just change battery if not you will blow the fuse

[@RobertSmith-di5ll]

If you hook up the battery charger it may draw too much and blow stuff - not worth the risk?