If you are satisfied with your results without a mask, then you don't need to make them, but it's a good skill to have in the kit.

I think that many of the contrast problems people have with Ciba/Ilfochrome come from using films that are oversaturated or excessively contrasty. I used to get nice Cibachromes without contrast masks usually on pearl surface Cibachrome from Agfachrome 100 and EPN transparencies--relatively neutral films that picked up just enough color with Cibachrome without turning into the "glossy placemats" that Sandy King referred to in another thread, and which could be identified as a characteristic "Cibachrome look."

But try to print Velvia or Ektachrome 100VS on Ilfochrome without a mask, and it's no surprise that the results might look a bit overcooked.