I have problems with my system, and I haven't found any solution to them. To solve them, I decided to reinstall the same system, there's an option that says something like "install the system but saving the documents" can I trust it? Will everything stay the same? Help.
Have a look here https://help.ubuntu.com/community/UbuntuReinstallation
Conclusion: It is safe, but you ALWAYS should back up anyway.