I’ve never liked writing advice that was “Nothing should be described outside the main plot. If it doesn’t pertain to the plot, delete it.” Now this may just be a preference, but don’t delete scenes with the characters family interacting or the main character struggling with their homework or wishing that they could be doing tests instead of saving the world! For the plot to have any impact or weight at all, the reader should care about the characters. The reader should see what’s on the line if the characters don’t solve the plot.
For example, readers would not have cared about Harry Potter as much as they do if there hadn’t been scenes of him just being a kid, struggling with school duties and such. Fred and George Weasley, the twins, being silly and running a joke shop is why Fred’s death had such an impact on readers. Because they acknowledged that the characters had dreams and a family. For the threat of Voldemort destroying the world to have any emotional impact on the reader, the characters he are threatening should have things on the line. Now imagine it without all the silly jokes and classes and stuff. Harry Potter goes to Hogwarts, immediately interrogates Snape, follows him, and the finds out about Voldemort. Without him being a ‘normal boy’ who was sort of forced into ‘the chosen one’ role, it feels stale and forced.
In the ‘Are You My Dad’ arc of Steven Universe, the whole entire reason the viewers were shocked when people of Beach City began to get abducted was because they cared. Nobody thought the human characters would be intertwined with the main story, even though it was their lives on the line. The show spent an episode developing Lars and his family, and then his love for baking, and fear of opening up. Just as he is about to open up to some characters he admires. He disappears. And other characters start disappearing until it’s revealed the alien characters have been abducting them. This had weight on the viewers because we spent time with them outside the plot, having fun episodes and silly moments where the characters weren’t focused on the storyline. If every series was a serious main character saying ‘we have to solve this’ without any weight or emotional impact, or stakes, then almost all series would be stale and mean nothing to the viewers.