If you ask yourself what phenomenal consciousness is as part of the larger system of the mind, then one possible answer is that it is a planning centre able form plans based on one or more data streams/channels of your choice. Each data stream/channel is one of the phenomena available to you in real time in consciousness. But you can't focus on them all at any given time so you focus on what's important to the task at hand, with the act of focus itself being the means to connect these disparate channels into a coherent plan. For instance you focus on a memory of something to look for, then you might have to focus on action to move your body or eyes to search a scene for it, then you focus your attention within the visual field of your eyes etc. So if it is something like that then I would assume that any phenomenal channel in consciousness has a reason for being there, including the sense of will. So the question is, what does it signal? And one possible explanation is that it is present to signal that the 'plan' is working as intended. But if something like a reflex action interferes, which you did not will, it alerts you to the fact that something outside the considered plan of action might have affected the plan, so in that view it could be kind of like an error signal. Just musing here - please ignore me if I'm not making any sense 
