One of basic things you can do with real watercolor is re-activating dry pigment using water.
I haven't found any way to achieve it with Rebelle after drying or fast-drying the layer.
If you are aware of a good way to do it, please share.
To give a bit more practical example:
Let's say i have a hard edge in my painting because I put a stroke of watercolor over already dried layer of pigment (and dried it again). Now I want to blend this edge. If I use Blend or Smudge tool, the pigment will not be affected by paper the same way as re-activated wet watercolor would be (e.g. paper texture shows differently). Using water also doesn't help because dried pigment seems to be permanently "baked in", smudge & blend do not react with water.