The evidence for it is purely anecdotal.
I took glucosamine sulfate for a few years, starting about 2000. The glucosamine/chondroitin mix works a lot better for me. MSM is another additive, as is hyaluronic acid. MSM was largely useless either way, hyaluronic was a bad choice for me.
I still take the gluco-chon triple strength, 1x/daily; I can tell the difference after a few days if I don't.