First, it would be easier for people, especially children, to learn. And second, it would be easier for people with a disability to use.
Yes, yes, we all know that there is nothing on this planet that wouldn't be better if Kintaro invented it.
It also means that it is easier to develop viruses for Windows.Mac and Linux = almost impossible to get a virus (but it is possible.)
Windows = Totally fucked it up for years by giving users automatic root accounts, has improved since this time, putting serious investment into developing new relevant technologies.
OS X = Inherited a secure system and takes security seriously but perhaps takes their own security more seriously.
GNU/Linux = Security enthusiasts taking control of the system forever, bugs are dealt with completely transparently, changes are pushed through to users as a first priority.