There are a lot of ways to use IC Concern of Preconscious. And I’m sorry I don’t totally understand what you mean by “plot” here, so I’m going to have to wing that.
If you look at a story as a character pushed to their extremes—which makes sense because what other series of events would test their way of doing/being—then what a concern can mean is not exactly their personality but rather how one corner of their personality is being forced to the surface.
But it’s not always so direct. Let’s say your MC (the CEO of a company) witnesses a manager annoy his underlings. The manager might not specifically be expressing Preconscious—maybe he’s just a huge jerk, but people stomach it because they don’t want to lose their jobs. So the underlings grin and bear it: they use Preconscious to repress their desire to lash out.
In this case, we’ve witnessed a personality and preconscious but they’re not the same thing. It’s just the fabric of the story.
In the same set-up, a benchmark of subconscious could be the underlings’ desire for respect. It could be the manager’s need to fear-monger.