How can I hide the Shipping Rates Calculator Plus widget?

It is possible to keep the widget hidden by default in order to avoid interference with your customer's loading process; the app will place a toggle so the customers can freely decide whether they want to see the widget or not. This can be achieved by going into "Advanced Preferences" and looking for "Toggler Accordion". By default, this option will be set to "Don't show toggler" and have the "Show the app widget initially when the page loads" option ticked.

You can then select where you want the toggler to be displayed from these options:

Additionally, when you've selected one of these, the option to show the widget initially will automatically untick thus the widget will be hidden by default, only the toggler will be visible:

This way, for your customers to see the widget, they will have to click on the toggler. 

If you want the widget to keep showing by default but for your customers to have the option to hide it if necessary, be sure to tick again the "Show the app widget initially when the page loads" option: