I am a professional software developer of many years learning scala for new commercial project. Primarily I'm learning from Martin Odersky's book.
Whenever I veer onto the internet to find out why I should learn Scala the general theme is that it's a steep learning curve but worth it as X,Y,Z reveals itself.
I believe this is probably true and will preservere, however 14 chapters in and I spend most of my time viewing Scala as a command line application that runs in java. To date, and in the context of already knowing java, I would describe Scala as "unnecessary"