So far we haven't really seen the whole effect of a lot of branching and a lot of stuff happens on every route but how it got to that point changes depending on what choices you make. Some chapters branch more than others, like the last chapter had 3 different branches for how you resolve a crisis. The crisis is resolved either way but we have yet to see the overall impact of how the mc resolved it. It is 100% impossible to get every scene on the same save though, some scenes only happen based on what background you pick and there is a political marriage the mc has later where you're given the choice of two princess and you obviously only end up married to one of them. The other one disappears from the game after you make that choice and returns home.
Although I'm kind of confused what you mean by replaying. For every route based VN I've played I just make multiple save files and play them in tandem. I don't restart the game again from the very beginning each time. I typically have a preference for one the routes though and the other routes are usually more for me to see what I missed. Though sometimes I switch which branch is my main. For every Renpy game I recommend having multiple saves
