I created a little jsFiddle to play around.

http://jsfiddle.net/gjeiziner/TJYNN/

What I gathered so far:
1) If you use transclude with a directive that has no template, the element and its children will disappear from the html when you don't use the transclude function passed into the compile function
2) Transclude only gives you the option to re-use the existing element (where the directive is defined in html), including its children through the transclude function passed into compile. If you don't use it, then the element (including all its children) will be lost.
2) If our ga-map directive would have a template, the template would remove all child elements 

Alot more to find out