In ContentBrowser click right mouse button and select option

Material Data: Material that will be used to generate Texture

Width: size of generated texture

Height: Size of generated texture

Parameter values: mapped from materialData at first time. Can be modified that allows to create customized texture output

Most of the size is thumbnail generated by Unreal Editor and stored together with asset Data

any material that has EmissiveColor output can be used for texture generation

User Interface domain materials also can be used to generate Procedural textures

Even 4k textures has size about kilobytes on disk.

Using materials with several Texture parameters allows to create Mattexture2d assets that represent textures with several layers combined.

Material Interface to Material Instance Dynamic:  Create  new instance  of  Material or MaterialInstance

MaterialInterface to Texture2D: Size of texture generated and Material that will be used for generation. Create in Memory Transient Asset UTexture2D

MaterialInterface to MatTexture2D: Size of texture generated and Material that will be used for generation. Create in Memory Transient Asset UMatTexture2D