I like back stories in very small amounts becuase a character’s behaviour and thought process often reveal much of their past.
Many books I have read have back stories that are too obstructive. There are even books out there that are mostly backstories and very little actual story. I also quite suspect that backstories are used by many books to cover up the lack of actual story/plot of their book.
Still it might be interesting to know some adventures the characters have in the past.