An RFI is a direct line to the designer, construction management, AHJ, and owner as to any questions/concerns you have about very particular aspects of the project. It is THE best way to protect yourself, and accomplish the task at hand.
If the plans call for a disconnect that you can clearly see is going to be covered by ductwork, you can ask for clarification. If they tell you to mount it as shown, then they will pay you to move it later... see how it works?
If you see a discrepancy, it's a whole lot better to clear it up before it becomes an issue, can result in an extra that is documented. Of course, it can also result in a credit, but at least you would not have to do something twice, spending your man hours a lot more wisely.
It's a good system where properly administered. I've unfortunately also seen it not done well where some arrogant designer took it as an affront that some lowly tradesman would DARE question him.
The larger engineering firms most certainly do not play it that way and really appreciate the input very much. How you phrase your questions has a lot to do with it, so kinda be careful and all the info passed along after that will be taken as valuable.