Even if it isn't necessary for supporting characters to have big impact, the main reason why this seems like such a waste of screen time derives from the fact that both the male and female lead are so devoid of personality that anyone with common sense would think that these episodes could've been used to nurture these two NPC's. It's amazing how even though they haven't done anything bad, it's really hard to be empathetic with them or to be genuinely interested in their so-called problems.
I'd say the worst part of this title resides in its last two episodes. We see that the male lead actually works things out and realizes that his high school crush was just that, a crush that was basically fed off his teenage desires and his frustrations as a young adult. He makes the right choice and decides to end on good terms with her. Surprisingly enough, she also decides to start acting as an adult an reciprocates this decision, these two adults in their mid 20's, after 10 episodes of acting like teenagers in spite of two actual teenagers requiring answers and guidance from them.
If "Yesterday" had ended in this episode, this would have been decent. But sadly that wasn't the case, for some reason they thought that the male lead deserved a happy ending, not taking into account that this would mean throwing all character progression down the drain. The main victim ends up being the teenage girl who was actually the only character that one might end up caring about, since her infatuation seemed to be a little more than that and objectively, she was in a much more vulnerable position family-wise than the rest of the characters.
To conclude, I would just like to point out that you should disregard any other review that compares this title with Kuzu no Honkai (Scum's Wish). KnH might not be perfect and it has its own flaws, but comparing it with this title can only be taken as an insult induced by a severe lack of proper appreciation skills.
