ATTENTION CHEMISTS! Good lab practices?

I am taking a college organic chemistry laboratory class. Today in lab we were given an unknown solid (crystal) organic substance to test in various ways. Then we were given 7 known substances to test as well to figure out which one of these our unknown was. Once we thought we figured out our unknown, we tested that known chemical in the exact same tests as we did with our unknown. We got all the same results. This obviously confirms they are the same substance (we did IR spectroscopy, for one.) But then our professor told us to MIX our known and unknown together and repeat all these tests again. That was very strange to me. Why would we do that once we had already confirmed that they are the same? It's redundant. And also, isn't it bad lab practice to mix an unknown with other substances just to test to see if they are the same? Even if this showed we didn't have the right identification of our unknown, it would give us less information than testing them side by side, and for another thing it's DANGEROUS. What if they weren't the same and they reacted together? Especially since in some tests we add heat (melting point)!! Am I right in thinking these things? Has anyone else done this or heard of these practices?