I think about them, but I never want it to be shoehorned, since sometimes a character gets full on deleted and I have to have someone take the place of two characters--also not every character needs to have a character arc? Not every character needs to take the limelight with their own personal anime arc or my series will be like a billion books long.
So I've been working on this script for a comic that I'm making, where I basically decided...to not write this one flashback. I put it off for 6 drafts. I've already even started making the comic episodes because I just assumed my story was solid and I would not write this particular flashback and leave it to the reader's imagination since my story was already pretty long for a comic.
But to summarize a complicated story, I realized that a 3 year gap should probably have some sort of filling out, especially since there's romance in it and people may want to read that. So, as I played around with what it could be, testing out different scenes and ideas, I recognized it was a place where some of my characters could be night and day to how they were in the current timeline. And I did that mostly because I thought it was interesting, and no other reason. It was not planned.
But it also made a place where the flashback became something a lot more important to the overall story. I was able to flesh out other characters and the reasons why they were different 3 years ago, but also the same. It basically gave me a reason to care about this flashback at all, and that's why the character development is there. If it makes me care about the story, then hopefully it will make my readers care as well, 4 years from now when that certain comic episode goes up (ah the pain of making comics.)