For example: In Pokémon Fire red/Leaf Green we need to catch a certain number of pokémon to be able to have access to some items like exp share for example, in Pokémon Sun/Moon/Ultra Sun/Ultra Moon we need to have a certain number to be able to unlock everything on the Poké pelago, in Pokémon Sword/Shield we need to have a certain number of varied types to be able to do the Poké jobs. I'm talking about these kind of things that has a high level of importance, not small things like needing to complete the pokédex to have a diploma, or shiny charm, things like that.
The purpose of this question is to help people who have this doubt to be able to plan ahead on their first playthrough, to not face situations like: The player decides to catch only the pokémons he will use, further ingame he realises he needed to have caught a lot to make use of something important on his gameplay.
(By the time i'm asking this question i'm one of the people who has this doubt)
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(My english is not the best, so I humbly ask anyone that can edit this to edit the grammar mistakes if it has any, thanks!)