- Not get relevant answers.
- Consider many things to be understood a priori by all parties involved because "real pros already know all these simple things" - Do I need to say how wrong that is? How all people see things differently because they had different experiences?
- Miss ideas, suggestions. All unspoken words are a missed opportunity for lateral thinking.
- Be considered uncommunicative or, sometimes, even worse: arrogant or stiff.
- Understand things the wrong way, get wrong ideas, do wrong things.
I guess that, if one is in the room, probably he/she is there because someone has confidence that he/she has something to say so why not say it?
VERY IMPORTANT: no to fall to the other extreme: speak all the time because you think you have all the answers and have the right to monopolize the whole conversation. The point for asking questions is to let others speak and gather information from them by actively listening to what they have to say.