I restarted my games quite a bit during my teenage years - I'm a chronic planner and I constantly had new ideas for teams across all my games, but I'd never finish the story! I'd get to the mid-game slog and just... restart, seemed like I got more joy out of planning than I did playing. It unfortunately led to me restarting my Pearl file which had 300+ hours in, a HeartGold file which featured my most iconic Johto team, and a White file where I cleared everything up to Alder (which also held a bunch of Pokemon I transferred from my Gen III / Gen IV games). I regret that a lot, but what's done is done.
Nowadays I'm keener on actually having my save files maintain longevity and act as foundations for future playthroughs - multiple save files on the Switch enabled that! Plus I'd like more hours on my Switch anyway so fully completing my games seems like a wise move. I'm only at the Galactic Warehouse in Brilliant Diamond but I'd like to clear that game, finish the Pokedex, clear Contests as far as I can, do the post-game and conclude all possible gym leader and Pokemon League rematches at their highest level and beat Palmer at his strongest (not so much the Battle Tower overall). When I get to SwSh I'd like to do both DLC, the Galarian Star Tournament, a full Pokedex, beating Leon at his most challenging in the Battle Tower and whatever else is possible. Things like that.