One of my favorite slogans at a famous DIY rental business is: "Together, we can do it yourself," and it reminds me that both the left brain and the right are crucial to the modern commercial or film composer.
A composer needs to have a bipartisan brain effort to be successful. The left brain and the right brain need to work in concert for any successful musical endeavor. Even though it's often just li’l ole me generating all of the music, I can't do it alone :)
In the past, the steps to realize music were often divvied up between many individuals, e.g. composer, arranger, orchestrator, copyist, producer, engineer and musicians. Most of these hats need to be worn by one person now. There's a lot to know and a lot to manage, and that's why I break up most of my tasks and assign them to the left brain or the right brain.
We've all heard the old cliché: "Musicians are good at math." Well … maybe. Don’t ask me to recite the binominal theorem, but I certainly incorporate math when I am fitting music to picture, copying notes to a page, and defining an overall structure to a musical piece. The modern musician needs computer skills, file management systems, and the ability to manage time. S/he also needs clear concise briefs from clients. These all involve the left brain. I write out my plans and make my lists. I write creative briefs to myself.
The modern musician also needs to be free and spontaneous. S/he needs to follow intuition and hunches. A modern composer needs to be provoked and needs to ask questions. Composers need to be their worst critic and their greatest fan. Every performance must be full of intent and feeling. I have to be sensitive enough to know when my composition has a soul.
So, we need both sides of our brain firing on all cylinders to create music that is both appropriate and special. Agencies and people commissioning music need to know this when trying to articulate what they want. My clients will get better results knowing that, even though I was born and raised in New Jersey, English is really my second language. Music is my first. We need both sides of our brain satisfied to create music that people are willing and happy to purchase.