Fantasy series seem like they've gotten longer and longer and it's often years between volumes. Many authors have started doing recaps of their previous books at the start of later volumes, but not all.
I use LLMs for that all the time. Most frontier models have books trained in, so I just ask for a spoiler free recap or ask about certain characters. Works well in my experience, and made jumping back into Wheel of Time a lot easier
I could see this being useful for that.