You know the concept that people are nostalgic for their formative teenage music and TV shows because the memories are so deeply ingrained that re-experiencing them releases dopamine? Another way of considering that phenomenon: variety. After all, people love trying new things. Vacations are an example, as Frazz points out.
At first, nostalgia seems like the opposite of variety. But it’s not. If you try thinking fourth dimensionally, your life becomes a line of events. You travel through it linearly, with no chance to shake things up by shifting to a new age or experience level when you feel like it. Flashing back to your past when coming across a floppy drive or episode of Pokemon? That varies your mental experience.
The basic point here is that it’s not healthy to constantly live in the present. Thinking ahead about where you might end up in ten years or reminiscing about childhood times solving Encylcopedia Brown stories add variety to life. People complain about the pitfalls of nostalgia, but the pitfall is banality. Those who spends all their time in the past are just as unhealthy as those who spend all their time working in the present, all their time daydreaming into the future, or all their time rooting down for staycations.
Fight the tyranny of the fourth demension!