The way I find it easiest to understand the dichotomy of this pair is to answer this question:
Do you feel more comfortable after you’ve made a decision (J) or before the decision is made (P)?
Judging people (not to be confused with judgmental people, which this is not) are usually task oriented, put off play until work is done, make lists, are comfortable when decisions are made, and hate having the pressure of looming deadlines so will carefully schedule their work. Sometimes they focus on the goal so heavily they miss (or ignore) new information which could impact them.
Perceivers like to keep their options open. They often don’t make plans and will decide when they must (and sometimes they will miss out because they didn’t decide). They tend to work in bursts of energy, often becoming more energized as a deadline nears.
My better half, Jan, is a big-time J. I am normally a strong P with the distinction that when a decision needs to be made, I make it and move on. Until that point, my theory is why not collect as much data as you can? (Pure P thinking.) Jan, of course, is going crazy while I check out “just one more thing.”
One reason we read novels is to learn how characters act under stress. Stress can be physical (someone’s trying to kidnap me!) and those confrontations can rev our endorphins in sympathy with the character. But if the only stress is action-oriented, most readers soon become bored (unless we channel our inner teenage boy). Mental stress comes in all shapes and sizes and can hold our interest throughout a novel.
Jan and I are currently looking at a major decision, and I can attest to the building tension when a J and a P must jointly make a decision (assuming neither one is the type who rolls over and capitulates with “whatever you want, dear).
It’s also interesting to see what happens when the author forces a P character to make a decision before they can gather what the P thinks is enough data. After they have been forced to make it, how long will they rehash their decision before they accept it? What form does their regret take? What happens in their dreams?
Or consider the mental punishment of not allowing a J who has decided what should be done to enact it. Or what happens when against advice (probably from a P) that they should consider other information before deciding, they go ahead, only to discover they have made a huge error?
As an author, I find satisfaction in torturing my characters and seeing if they grow stronger or crumble under the stress. As a reader, I want to know what’s going to happen.
In real life, it’s not quite as enjoyable, but it’s easier for me to cope when I can reflect on everyone’s style and how that drives the way they see the world.