Exclusive Missions for the main quest

[Main quest in this case refers to missions along the critical path (i.e. missions that MUST be completed in order to finish the game)]

There may be a better term for it, but when I mention the term "exclusive missions," I'm referring to moments during the main quest where you make a choice and it leads you down one particular mission type; making the other mission no longer playable. An example of this can be seen in Dragon Age: Inquisition, where if you choose to recruit the Templars you'll be given the quest, "Champions of the Just," while siding with the Mages will give you the mission, "In Hushed Whispers." Depending on which side you chose, the other faction mission is no longer available for that playthrough. Another example (outside of BioWare games) is with Deus Ex: Mankind Divided, where you choose to either steal a chemical substance from a bank vault (to prevent a chemical attack), or you can go after the sister (and bomb-maker) of the games main antagonist.

For some players, these missions are enjoyable because it forces the player to have a make a well-defined choice (with not many other options), and the events that take place inside this mission can often have reverberating impacts throughout the rest of the main campaign. This also leads these players to try out multiple playthroughs to get different perspectives of the story, world, and/or characters.

On the other hand, some players dislike this feature because it feels like they are being punished by not having the opportunity to experience everything the game has to offer; in one playthrough. For relatively lengthy campaigns, this could mean spending several dozens - if not hundreds - of hours just to see the other side of the campaign.

From a developers standpoint, this likely leads to significantly more work, as you're essentially building multiple stories into one game. Depending on budgeting and development time, the settings in which these exclusive missions take place, how much the narrative differs within these missions, the impacts these missions have on the main quest, and how many choices the player has in each of these missions, can vary drastically. While, ideally, a developer would like each of these missions to be as distinct and pivotal to the campaign as possible, realistically this isn't always the case.

I think for me, I don't mind there being a good number of missions like these, so long as it makes sense for why the choices are so binary; or limited.