Safe Mode is just what you would expect-a secure way to boot up a PC and run the system without startup apps and only essential drivers, which should hopefully allow the computer to boot effectively when it won't otherwise because of some problem or other.
If you're preparing to migrate to Windows 10, the first thing you might possibly run into trouble with is actually downloading the OS. It takes a certain amount of free space on your drive to install a new operating system so that it can be updated and certain components can be effectively managed.
