My page history is gone, or my Pages -> Template connection is broken
If you edit a template, each time you save the template, it will create a normal revision in ExpressionEngine (assuming you have template revisions turned on).
However, if you overwrite a template on your Mac by dragging an identically named file over it, or if you overwrite a template group by dragging an identically named folder to the Mountee drive, you will be assigned new template IDs and you will lose the the revision history of any affected templates. Your new templates will still work normally. But if you want to keep the revision history, it’s best to edit the templates directly instead of by overwriting.
You will also switch back to the default template settings for caching, PHP, and hit counter.
The Pages module also uses template ID to connect an entry to a template, so we recommend you don’t overwrite Page templates.
Note, though, that this is a great way to kickstart a site, by dragging and dropping a pre-made group of templates, snippets and variables to a new site.