When you are writing node content programmatically via a module you may run into the question of how to customize the screen output. Especially if the output from your module is not in a human readable format like JSON. In Flame's Blog, Prajwala shows how to direct calls to a template to the modules directory.
I decided to use my custom block.tpl.php which is there in my module. But by default drupal will load block.tpl.php from your theme. If there is not block.tpl.php in the theme then it will load block.tpl.php from the block module.
Be careful with this and use it only if you want to override custom templates used by the module, not standard templates in your theme or core.