Having another UV set or essentially an additional Material ID will result in an extra draw call per frame. I wouldn’t recommend going crazy and having everything have three or more UVs/Mat IDs, but the occasional object is not going to be that big of a hit. Another thing to consider as well is texture resolution and whether the texture is a power of two. Again, having that extra draw call for that material ID slot will be added and having a larger texture for it will result in a heavier hit.
I hope this helps!
Tim