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.