In some scenarios it is recommended to pre-load resources.
This is mostly needed for high resolution images, audio files and web resources in general.
Pre-loading resources can help to remove possible image flickering or audio files not starting fast enough.
It is also recommended to pre-load animations (FMA files) to make it play smoothly and not lag or show a black screen when first loaded.
To add a resource to FancyMenu's resource pre-loader, just click on Pre-Load Resources in Customization.
This will open a menu that lets you add local resources, web resources and resource pack resources to a list.
Every resource in this list will get pre-loaded every time the game reloads its resources, so basically every time the resource loading screen is visible.
You can also add slideshows and panoramas to the list of resources to pre-load, which will help fixing issues with panorama or slideshow images showing as black/missing image first or flicker for a moment.