I am a discovery writer (aka pantser, but I dislike that term). You can see my approach to starting a novel in this answer to a different question. I'd also recommend this other answer that talks a little about story structure.
To answer your question, I never write extra scenes to explore characters, the novel IS an exploration of the characters. The whole point of discovery writing, for me, is to NOT get burned out.
Thirty years ago, I tried plotting novels, after my third attempt I gave up. The problem is not the plotting, I developed good plots I liked. The problem was the plotting burned out my enthusiasm for writing the scenes and details and dialogue. My characters seemed artificial to me. I spent so much effort on the plotting, going over it again and again, that writing felt like work, or felt like watching a movie for the fifth time in a row on the same day. It was not exciting to me anymore, I didn't feel like I could change the characters without damaging the plot, so I gave up on that approach.
IMO writing "extra" scenes to get to know your character is a plodder's strategy (oops, I meant "plotter"). I begin with a character, and she is going to have a problem. She will also have friends, a job, perhaps a romantic life, etc. I don't write ANY of this down. I am usually obsessed by this character, and spend about a week thinking about her, her reactions, her day-to-day problems, what she finds fun, whether she is sexually active or not, or wants to be, where she has been, what she hopes to be, if she thinks ahead at all. I think about her in traffic, at lunch, at work, at dinner, even watching TV or reading, she will make comments in my head giving her opinions.
But I don't write it down. To me, writing releases the energy of imagination, I don't want to do that. I just want to know her. When I write, I have some opening in mind for her, some little problem (not necessarily part of the main plot) she has to solve, that reveals something important about her character. The first thing I write is her name, and she will be in action, doing something. The first 1/8th of the book is all about her normal world, not about the main problem, just so the reader gets to know her, through her actions and dialogue with others. We meet her friends, coworkers, acquaintances. About 1/8th of the way through, we have the "inciting incident", about 1/4 of the way through, this has grown into the major problem of her story, and it forces her to leave her normal world -- mentally, metaphorically, or physically, and sometimes combinations of those -- in order to do something about it.
Follow the basics of the three act structure (see second link above), without plotting. Let your character react and develop, she is not static. She can learn things, her friends or allies can learn things, and new things about her. I know, because I have internalized the three act structure, basically the kind of thing I am working toward, and how many pages I have to do it.
I do always have some rough ending in mind, which I write in sketch form. No dialogue, no prose, just the basic facts of how her story gets resolved. I treat this like a compass direction. But it is changeable, if what I am writing is going to preclude that ending, my personal policy is I have to come up with a different ending at least as good, or scrap what I am writing and start over, avoiding the dead-ending.
This is not an "efficient" or "time-saving" approach to writing! I have scrapped 5000 words I wrote that led to a dead ending. I have scrapped my first chapter in more than one novel, and started over.
But because I have NOT plotted, I am discovering the plot as I go, and I don't burn out. Also, at every new turning point, I can invent that for how the characters are at that point in the story, so they don't feel forced or unnatural in their decisions. And I actually like inventing challenges that might alter their character in some respects, I don't mind at all if my characters evolve as they go. That's how real-life works too, we are all molded by our experiences, so why should my fictional characters be any different?
I don't draw maps, up front, I don't write character bios. I do keep maps, as I am writing. If I need a lake or mountain range or river, I check my map-so-far to see where I can put one in. I do keep character bios in a sense, if a character reveals something important (their age, sexual experience, biases, likes, dislikes, traumatic experiences) I keep a note on their bio and may consult the bio to make sure I am not introducing an inconsistency. But that's it, I want the physical map or setting to be consistent, and I want the characters histories to be consistent.
From one discovery writer, that is how discovery writing works. It keeps me interested in the story, from start to finish. I do review my finished story, several times with much editing, but the story is complete and I am getting ready to send it out, and that is exciting too. I feel like I am strengthening it.