I don't chime in on these "should I learn music theory?" debates often, but I have a little time and may be able to shine a little bit of light from my experience here. I'm sometimes one of the people who has a music theory background working with those who do not. In my experience with larger projects, there are generally two types of people who don't have a good grasp of music theory:
- those who lack knowledge but understand and accept their limitations and attempt to put in place procedures to allow others to assist them in the most efficient way possible.
- those who lack knowledge but either try to hide that fact or continually insist that it is not necessary.
People in both these categories face additional hurdles in realizing their musical ideas. The process of creating music is more challenging for them because they must go through a lot of trial and error. More knowledge would enable them to understand what they want to do and make better decisions from the start. It also means they have more difficulty understanding the potential pitfalls and costs of their decisions farther down the creation process on larger projects. That can get very costly and cause a lot of stress for anyone who works with them because time and energy becomes focused on things that have little (or negative) impact while ignoring the things that may greatly help reach the artist's or composer's desired goal.
The people in category #1 usually have enough experience to be cognizant of these challenges and do their best to minimize the negative outcomes. Usually they find good, skilled people to work with them, give them clearly defined roles, and then try to stay out of the way of those roles and trust in the professionalism of those on their team. They usually understand that they are often the source of backups or other issues, accept that fact, and structure their schedules and resources to account for that.
The people in category #2 are often a nightmare and skilled, experienced people sometimes will avoid working with them. I've dealt with people in category #2 in a number of situations over the last 20 years: films, stage musicals, album recordings, TV shows, the big award shows, and live concerts. These are the people who because of their lack of knowledge often talk on and on about being innovative while doing things that have been done dozens of times before in exactly the same way or perhaps even more elegantly. They often want to rewrite all the "rules" without understanding what the "rules" are or which rules can't be rewritten. (Music is sound which is governed by the laws of physics.)
Category #2 also contains the people who will hire very skilled professionals, sometimes the best in the business, and then second-guess every musical decision those people make in trying to efficiently realize their musical goal. They will demand costly, time-consuming changes that have little to no impact on the final music. They are unable to see when they are doing things that will have musical outcomes different from what they desire. Most devastatingly they will dismiss the advice or decisions of their own experts who are there to help them because they lack the knowledge to understand the advice they are being given.
Category #2 are the first people to see advice, even when it helps them reach the exact musical goal they desire, as compromising their creativity or forcing them to accept certain "rules". These are the people who cause others working with them to stay up late and burn themselves out doing things that ultimately will have to be changed later or just won't work at all. That can be soul-crushing and cause even the very best among us to either walk away from a project or simply turn into robots who blindly follow every instruction even if they know their work is harming the composer's vision for end product. No one will listen to them anyway because their knowledge and experience is worthless when ignored.
Music is like language. It exists to be heard and understood in some way by a listener. You can communicate effectively with others without a good understanding the grammar of your language, but as you try to communicate with wider numbers of people or convey more intricate and intimate ideas, the lack of language resources will limit your capacity.
Having a good musical foundation in theory, harmony, ear-training, etc, benefits you more the further you progress in your musical journey. As you progress you will most likely have to deal with other musicians. This is where the gaps in someone's musical knowledge start to become a problem. They limit your ability to communicate your ideas or make effective musical decisions.
Those are my observations from a rather varied career so far that stretches from little student projects to major record label productions, to blockbuster films, to the Oscars, Grammys, and Emmys. In that time, I have never seen having more musical knowledge be anything but an asset. More musical knowledge puts more tools in your bag that you can pull out when needed. Usually having too little knowledge is the biggest problem. As some of my colleagues like to joke, far too often people "know just enough to be dangerous to everyone around them."