Because of the Registry Tuner data files are composed from miscellaneous sources and miscellaneous authors, and it is impossible to test each of a registry keys described in it, the program authors do not bear the responsibility for functionality of keys or for caused by them of injury to your operating system. Registry Tuner data files propagated together with the program are free of charge, aren't the property of Registry Tuner program authors and are not object of sale and purchase. They deliver "AS IS". See the LICENSE AGREEMENT / WARRANTY DISCLAIMER.
It is always a good idea to backup your registry before making any changes to it. It can be intimidating to a new user, and there is always the possibility of changing or deleting a vital setting causing you to have to reinstall the whole operating system. It's much better to be safe than sorry!