This is the texture that controls shine/gloss in Sims 4. If you don't want your object to be a shiny beacon, fix the specular!
Sims 2 to 4 Conversion Tutorials:
Part 4.3 - The Specular
The RGB Specular is how you control the shininess or matte appearance of an object. You can apply different settings to different parts of the mesh such as the fabric on a bed and the wooden parts of the bed frame to give them different levels of glow or shininess.