Polymer app best practices

I have best practices questions to respect while developing Polymer Web App.

Let's say I have a Todo app. The main element my-main-task is responsible for switching between those elements: list all tasks, view a single task, create a new task, edit a task and delete a task.

My question is: the new element must save data using firebase-document or iron-ajax by itself or delegate it to the my-main-task?

Thanks for your help.