What is the recommendation for working out while sick?

I hear so many vary opinions about this topic. I went to the gym to do a light cardio session. I only really had a sore throat but I felt like I was trudging though mud, and I am someone who works out frequently so I am not out of cardio shape. I was speaking to someone and was informed that when working out while sick or getting sick you are reducing hurting yourself because you are using white blood cells for muscle tissue damage that could otherwise be used to help resist a viral or bacterial infection.