If you're the type who would rather play New Vegas for the 8th time than load up a game you got last summer sale, science says not to worry! Yes, even if you make the exact same story decisions every time. That's because there's a thing called “Volitional Reconsumption” that validates your habits. Google has a few good resources on it if you want to learn through scientists [most of what I’m saying is from here] but otherwise I'll explain it in videogame-ish terms below.
“Reconsumption” is when you voluntarily “consume” the same experience over and over again. This obviously relates to repeating the same media [book/movie/song/etc] but it also relates to activities like going to the same place at a beach. It’s particularly common with “hedonistic” experiences, AKA fun/good/self-indulgent stuff.
So maybe you find yourself getting in a New Vegas mood every summer, or you tend to rewatch Steven Universe at the start of a new term. This kind of stuff, turns out, is actually good for you!
Why is it good? In the most general sense, it helps your mind sort itself out emotionally and it helps you become a more solid person.
Specifically, when you repeat an experience, it’s tied to all the past times you’ve had that same experience. Your brain navigates within/between your emotional reaction to all the other times you’ve consumed that thing, and then goes: “Hey, how is my emotional response different/similar to the last few times I've done this? How am I doing as a person this time? What does it mean, if my reaction is different now?”
The term is “emotional efficiency” – you “optimize” the search/attainment of specific emotional outcomes, because you know it’s already present in a certain game! Repeating an experience makes it a good control variable because you don’t have to scour the world to find another thing that can give you the same experience.
For example, if you are the type who replays Skyrim every time it comes out, every time you finish the Dark Brotherhood questline, your brain already anticipates your emotional reaction from the previous times. In repeating this emotional reaction on purpose, you get to do a few things:
A) use it as a gauge to better understand how you've changed since the last time you've done this. For example, are your feelings on Astrid / Cicero / etc different this time? This helps you see your own growth.
B) use it as "training" for your emotions, to make you better at dealing with that type of emotional catalyst whenever it arises in day-to-day life. So your brain will be a little better at coping with situations similar to the Dark Brotherhood's.
It also helps you get a deeper emotional scoop out of the experience itself, because you have a better chance at finding things you’d missed before… but the main important thing is that in the end, you become more aware of your own growth. You become more aware of your understanding and appreciation of intense or difficult subjects by using the repeated experience as a lens.
Final note: this is why you should let kids repeat stuff all the time! Repeating books, movies, games, etc. is specifically really great for children because they do volitional reconsumption even more than adults. So try not to get too annoyed when they do it... it can be good for them to a point, as it's how they develop their understanding of the world.
In conclusion? Don't feel guilty for supporting Yes Man for the 8th time out of 8 playthroughs. :)