If you change a texture's compression settings, materials will show errors because of a mismatch in the Sampler Type of Texture Samples.
This can be fixed by adjusting the Sampler Type and re-saving, but licensee complains that when doing many textures or a texture that's used in many materials, this could be a workflow hassle.
1. Create a material that uses a Texture Sample of a texture
2. Open the applied texture and change its Compression Settings to a different type
3. Note that Material now shows an error on the Texture Sample node (see attached image)
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-19653 in the post.