Musicon project, handlebar question, when to use {this} keyword

So I completed the Musicon project today but ended up with a question on handlebars. Since the question is very context dependent I hope maybe someone here (who has also done the project?) might be able to help.

Basically, I don’t understand when to use the keyword this and not. I’ve taken a screenshoot of my code which I hope can clarify my question.
Why shouldn’t I use this in the context shown i the pictures?

Thanks for any help!

Best regards