We're running Office 2010, but needed PPT 2014 to edit a client file, which we had to install from Office 365. After that everytime I tried to launch Outlook it demanded the license key, then "repair" -reinstalled Outlook 2010 in a never ending loop. So I had to nuke PPT 2014 to get Outlook back.

That's not an issue with O365 as such, though - that's obviously an issue Microsoft Office itself. They're not really the same thing beyond now being able to license them over the internet.

You'd have probably had the same thing if you'd installed PowerPoint 2014 from media.

You could have used the streamed version which doesn't install anything, though.

365 was the only option I could find on their web site after spending almost 2 hours trying to figure something out (was really hoping to add PPT Office 2010, but that was not an option).