Originally the story I'm working on had a host of flashbacks that I felt illuminated particular parts of my main character's past. However, those flashbacks were all within the 10-year timeline that the entire story took place in. While I felt like the flashbacks were beneficial to the story, I began to realize the timeline itself was disjointed. So I've combined a number of them into longer flashbacks that elaborate a bit better than the previous ones did.
Flashbacks, in my opinion, are useful in giving perspective to a story. We see what the main character is like in the "present" time of the story; flashbacks give us a picture of what they were like before the story.
The trouble with flashbacks, I've found, is learning where to place them and how to distinguish them. Transitions are one of the toughest things, and I have never been a big fan of the old trope of putting in dates. While I understand that dates are easy time markers, they don't have a place in certain stories, and there has to be a new way to identify such things. I decided to mention my main characters age as close to the beginning of the chapter as possible in order to give the reader an indication of when in time they are.
My suggestion, having used a lot of different methods for playing with time in a story, is to write it linearly first. Then, determine where the story really starts and see if there is an opportunity to put in flashbacks. Otherwise, don't do it until you've got a story that really requires them.