I active the publishing features in many of the sites I use to gain access to things like master pages, page layouts, check-in/check-out on pages, etc.
Here is a list of what features get added for SharePoint Online.
By activating the publishing infrastructure what features am I losing out on / being deactivated? The main thing that I know of is the ability to create a site template. What else is there? Or even a broader question, why shouldn't I use the publishing features?