KickstartCassiopeia has the option to show a popup.
A popup can be overkill, but also quite important to inform your customers. You could inform them on changed terms, changes in opening-hours, some kind of special deal, you name it. It is up to you to think of a suitable usecase and check if your popups have the effects you want hem to have.
Setting up a popup is easy, go to the tab popup, enable the popup and set the content. I would advise not to use this on all your pages, but make a copy of the module that holds all your settings, and publish it only on the page you want the popup to show, and only there enable the popup.