Hmm..not sure about rosewater. I think it's really moisturizing or something..
Vegetable Glycerine is a humectant, which means that it helps attract and hold moisture. When mixed with another moisturizing ingredient or even just water it helps optimize the moisture retention or your hair.
I use it in a spritz mixed with aloe vera juice and filtered water. It's my base moisturizer and it really helps soften my hair. Because I'm transitioning, it's really important that I keep my demarcation line moisturized and flexible and this does the job.
ETA: I use it on both wet and dry hair but never straight - always in the spritz.