There were a number of reasons to use masking. First was obviously contrast control. Something which
required an intense mask like Velvia often required a supplementary highlight mask first to keep the
sparkle in specular highlights etc. The second reason was color correction. Ciba has a lot of idiosyncrasies in this respect. Then you could control grain reproduction and edge effect, esp by masking to produce printing dupes. But 99% of the printing I personally did was from large format
originals to begin with. I'm glad I learned these skills and acquired proficiency with the relevant equipment. Ciba might be gone (well, almost).. but now I'm transferring the same skill set over to
color neg printing. Many of the details are very different, but at least I'm not starting from scratch.