1. You are not the priority - if a better option comes along (read: better paycheck) then you will be dropped quicker than you can blink. This is not personal, this is business. The danger is the timing of this.
2. Your network will be small. Attracting funding is hard, and reaching an audience as a small company is harder - especially if you are independent and not creating work as part of a theatre's official programme.
3. Very often you have a much smaller company of people than a production may realistically require. Actors have to double as stage hands, the crew have to multi-task in extreme ways, and everything has to happen on a tighter, shorter and cheaper schedule.
4. Every success is an extraordinary achievement. Every failure is the end of the world. Emotions run high. This holds true for all types of show though.
5. An extraordinary amount of work goes into what may ultimately be a very short run. And then it's all over.