EB: In our video preview, we sample a few early missions from the games first chapter to show off the different types of dialogue options presented to you, and how they may lead to the story playing out differently. Choices made during main quests will surely impact your story later on in the game, but those made in side quests typically result in another side quest to complete, but they still shape your overall story.
Source: N4G PC Assassins Creed Odysseys Expansive Dialogue/Choice System Preview | Entertainment Buddha