If what happened to the character in the past is that important, why not extract it and expand it so it becomes a consistent, reliable part of the book’s structure, instead of a temporarily distracting time bubble? Conversely: if the scene isn’t that important, why not condense it to a memory?
Personally, as a reader, I dislike the use of flashbacks. I find them disorienting and confusing. If the past was so important, why isn’t the story set then? If the past was not so important, why do I have to read about it?
This is one reason I found On Chesil Beach (by Ian McEwan) frustrating to read.
I have just finished Waterworld, by Graham Swift. A great book – BUT, I struggled to follow the various time threads. Not only does he tell his own personal history using jumps in time, but he interweaves the history of his family and history of the fictional fen location in which the book is set. In the end, he brought all the interwoven threads to a satisfactory merger and it came all together nicely at the end. However, with each dislocation in time, I felt a dislocation from the story (if that makes sense!). For me, it would have been a more compelling read without the distraction of the jumps, at least within his own history.
Just my opinion. Maybe I am a lazy reader?