I'm not a fan of flashback. It too often means the story stops dead because flashback is essentially dealing with stuff that's already happened, so there's no suspense about what's to come. New writers are particularly prone to either a) having a character staring at themselves in the mirror thinking about what happened the night before or b) having a character embarking on a long train journey and thinking back to the last time they went to Abersoch (or wherever).
But as I've recently used a spot of flashback in my current book, I thought it was only fair that I said how I'd used it and why.
The scenario: The main character wants to do something, her partner didn't want her to do it, but she does it anyway.
It was important for the plot that the main character didn't really register her partner's wishes. My choice was either: to write a short scene when they have a conversation discussing it or cover the relevant bit of the conversation in flashback.
The scene would normally be my preferred choice but I chose flashback because:
a) due to logistics, this conversation would have to be over the phone, and phone conversations are always a bit meh, and to be avoided.
b) there wasn't anything else really to do or say in the conversation, so it would have only had one purpose. This is not good for a scene; a single purpose scene usually lacks depth and conviction.
c) it was important for the plot that the character didn't really register her partner's wishes. In other words, she - my viewpoint character - wasn't paying attention. I would have to write a scene where she was trying to do something else while having the conversation (eg check she'd got everything she needed in her bag before going out or check her makeup or try to put a pair of lace up shoes on while having a phone conversation).
The simplest solution was to have her remember the relevant bit of the conversation at a later date. I chose the moment just before she was going to do the thing her partner really didn't want her to do which meant I could give her a moment of disquiet at the point when she was making the choice of whether to continue or not, while also making it clear that she hadn't taken on board his reservations at all. And that she independently had her own misgivings - but then events over took her and she goes ahead (well, there wouldn't be any story if characters didn't do things they later regret).
So using a short burst of flashback (and I do mean short, just a few lines) solved the situation - and added value to the story as well (making it completely clear she hadn't taken on board his reservations).