We display primary gallery where only images is displayed.
There might be the situation that the currently used theme do not have any sidebar but need to use Flexi widgets.
In such case ‘Flexi Gallery – Sidebar’ is available to use. Which will work same like other widgets container and sidebar is automatically visible at Flexi primary gallery page.

You can also use any other plugins widgets here which will be displayed at primary page & category page of Flexi.

There might also be some requirement that you wanted to remove currently used sidebar of theme and add Flexi sidebar.
Click here for detail.