What is the purpose of "connecting to the internet and playing online"?

Fire Emblem: Three Houses finally released in my region. Upon starting a new game, I'm asked to choose between Normal and Hard difficulty, as well as Casual and Classic mode. And after that, I'm asked if I'd like to "connect to the internet and play online".

From what I understand, the newest installment of the Fire Emblem series is, as always, a single player experience. So what exactly do I get for playing online? What features are only available then? What will I miss if I don't connect?

Solution 1:

According to the review here: http://www.nintendolife.com/reviews/nintendo-switch/fire_emblem_three_houses the online features are:

Ability to see where other players were defeated or defeated an enemy. Moving a unit to these tiles gives an item or experience. Ability to see which percentage of players picked which options on free days. Access to a minigame somewhat like Luigi's Balloon World in Super Mario Odyssey in which you must find a player in your monastery within a set amount of time.

Further, this wiki page: https://fireemblem.fandom.com/wiki/Fire_Emblem:_Three_Houses says that online play enables:

Students of other players online can appear in castle, selling goods or repairing weapons for a fee.