We assume this means that when a 10.1.1 update (or whatever the next update will be called) comes out, you will not be able to install the update unless you have previously installed this Security ...

There are a few reasons why you might want to reinstall macOS (or even Mac OS X). Perhaps your Mac is working erratically and you think that a clean install of the operating system might fix the issue ...

In the event of a serious problem with your Mac, you may need to reinstall your Mac operating system. There’s a simple way to do this using your Mac Recovery partition or via Mac Internet Recovery.