If you just want to see the main story and event dialogues, any mishmash of characters will do. If you want to complete all content, including challenge missions, you're going to need optimal teams and strategies. In between the two extremes, a better team will allow you to gather characters and items more efficiently from events. If you don't plan to spend money, events will be your main source of Gatcha tickets (used to recruit characters), so being able to farm those more efficiently is definitely useful even for casual players.
This is an important question, so I've added it to the guide. Thanks for bringing it up.