We often hear about focus. You need to focus on a particular area in order to grow that area. And it's true. Focus on something and you will become better at it. "What gets measured gets done" as the saying goes.
I'm not disputing that. My point is that, when you are in a small company, you need to be good at a lot of things. Broad is better at small companies. They don't have a lot of people, so it helps when their people are cross-trained in many functions. The more cross-trained you are, the more valuable you are to any small company. Therefore, the more likely you are to be needed and this promotes your own job security.
I started out at small divisions of large companies, and the incentive there is the same. You wear many hats and the more responsibilities you take on, the more valuable you are to your employer. I am a sponge who enjoys learning opportunities and was lucky to be thoroughly cross-trained early in my career. When I moved to management at smaller companies, I wore even more hats and became even more valuable. Today, I still enjoy learning new things and also mentoring others.
It's a path choice. You can choose to get your Masters or Doctorate in your field. This tends to make you a Subject Matter Expert (SME) in your particular field. You will likely remain in that kind of silo and/or industry your entire life. And you will have a great depth of knowledge in your field. There are many who choose that path and become quite content and successful. I don't begrudge anyone choosing this kind of path.
I've come to enjoy breadth over depth. I consider myself a Jack-of-all-trades, Master-of-Many. In small companies, you need to have a significant depth in multiple areas to be successful in whatever project you are working on. The small employer is wiling to provide this On-the-Job Training (OJT) to you if it helps them succeed and they have confidence in your ability to tackle different problems.
I once built an Engineering department from one non-degreed draftsman to a number of degreed folks, who were each specialists in their own areas. Our projects were too small to have teams of engineers working on them. We made it a point to cross train everyone. So a Chemical Engineer learned electrical, instrumentation and PLC skills, while the Electrical Engineer learned process and mechnical, and the Mechanical Engineer learned process, PLCs, structural, etc. After a while, ALL of the team, getting some help from each specialist, learned enough of EVERY discipline to handle projects on their own, tackling every discipline themselves. They only asked for help when something was particularly complicated, and those requests diminished as the cross-training increased.
I think if you ask any of those people, they would tell you that that was the most valuable training they ever received. I also think it helps if you are interested in a management path. When you are a manager, you will be more successful if you are able to truly understand the needs of each of the disciplines reporting to you. And the higher you go, the more broad you need to be in order to understand the needs of the diverse folks under you.
In a small company, you can progress to the highest levels and still be involved in every area of the company. Even though there may be some level of delegation, you may find yourself pulled into the details to help solve problems.
In large companies, the nature of the number of people involved and the number of problems to manage is so large that the shift to more delegation and less detail is inevitable. So many large companies break into specialty silos for particular disciplines. And they'll need SMEs to work in a structure like that in order to be successful.
There's been a lot of talk about how small businesses are the engines of the economy. I believe that. If you ascribe to this view, take control of your career and make a conscious effort to broaden your skill set. This will make you more valuable to any small business employer.