If you have the Portion of Sales campaign connected, then the answer is yes: you do need to display the Portion of Sales widget from Shop for Good on your store at all times. 

Since all donations are made through the DailyKarma technology and our donor-advised fund The DailyKarma Foundation, displaying the widget allows you to remain in compliance with corporate co-venturing and fundraising regulations as regulated by each state's governing body. By opting to not display the plugin, you are not protected from corporate co-venturing and fundraising regulations.