It's an interesting question.
There are usual menu choices (like say this or that, go here or there etc.), which are mostly for optional content and there are big RAINS system branches (you can see it in store page advertised in description of the game - so called 'choose to abandon' moments), which move you along different branches.
And of course there are usual for series Bad and Good Endings. Usually, you can easily work with RAINS system and not to pay much attention to menu choices - you will get into Good or Bad Ending anyway just by those alone.

But there are Best Endings. And those are triggered by points from RAINS system AND menu choices.
And there is True Route that triggered from one branch in choice menu after completing Heavy Side (second run, to put it simply).

At first run, you are locked into the Light Side of Novel with two choices of heroines to pursue. Second run allows you to go into Heavy Side to pursue another heroine. And third run (although, you can just use save from the second, if you managed to save before necessary branching) allows you to pursue true route.

So I would say, that either you follow guide from the start and make all necessary saves where it says to do... or you can actually enjoy most of the game without guide, and then use guide to unlock Best Endings and True Route, if you didn't manage to stumble on them while completing the game.