In regards to Supernatural, there are at least 3-4 instances in which I think the deaths and resurrections were impactful in some kind of way.
Sam dies at the end of season 2 and Dean sells his soul to bring him back. This also leads to the finale of season 3 where Dean dies due to his deal, and then being resurrected in season 4. First of all, Sam's resurrection only solidifies how the brothers need each other and have quite an unhealthy relationship. Sam has to spend the entirety of season 3 realizing his brother is going to die. It's one thing to lose someone, but to spend an entire year knowing it's coming? I think that's terrible.
Dean's resurrection in season 4 is unexpected, but due to him torturing souls in hell, he is brought back by the angels, specifically Castiel. Not only does this come as a shock to Sam, it also adds the introduction of angels. Without Dean, Sam also flounders and delves more into his abilities, drinking demon blood. This leads to future conflict down the line, and eventually to season 5 where they realize they are better off together. As someone already mentioned, it's an important part of the 5 season arc.
The third important resurrection would be their mother, Mary. While I'm not saying it was the best resurrection, to me it eventually led to one of the best scenes in the entire series; the one in which Dean tells Mary he loves her AND hates her. He basically tells her that everything started with her and their life is the way it is because of her deal with Azazel. To me, that very moment makes everything come full circle. Throughout the seasons, it feels as if the boys keep their mother on a pedestal at times, and that episode finally states the obvious. We literally wouldn't have even had the show or storyline without Mary's choices. It's the catalyst for everything.
My last one is Jack in season 15. I know this one is probably unpopular because a lot of people really hated Jack, but I adored him as a character. I absolutely loathed what they did to him in season 14, having him basically lose his soul, kill Mary, and then just be killed off by Chuck. His resurrection gave him the ability to have some kind of redemption, but also he became God, which led to the end of Chuck.