A matter of preference and choosing the order you do things to get a different picture of things. Perhaps you only want to do conversations with one character for a while to get a conclusive idea of what they are like. Really, it's not about if it's needed, it's about preference. The only problem is that if you can't sufficiently clarify that both modes allow you to unlock and see everything, then it becomes a problem and I already confirmed that there are some lines that you will never see in vn, lines that are not important like asking the character if they need anything and they say no in their own way. It's not much.Do I need to farm something in Sandbox mode? If so, it's probably made for these people. Because I do not understand why it is needed if the content in it does not differ from the VN mode.
Also if vn and sandbox differed, it would be unfair to those who only want to go through the game once with full completion.