I never used to do so and have flip-flopped on whether or not I care about natures and stuff. But more recently, I've really let my obsessive side run with it. In my last saves when I was a student I planned the team, picked good natures, even bred a Munchlax for one save. Then in 2020 I got really obsessive part-way through HeartGold - after resetting for a good natured Typhlosion, not caring that Togetic's was only neutral because it had Serene Grace, then adding a Gastly and Machop to break my rules on using Pokémon in the game they're introduced because they had good natures, I ground my game to a halt to obliterate the Safari Zone so I could breed an Eevee (Vaporeon) and Marill with egg moves.
My Black save was part-planned, with natures and IVs steering me, but going back to Gen IV I bred my entire Platinum team - perfect IVs in relevant stats (so 2-3 stats), egg moves, natures, abilities etc. then EV-trained them using the Little Cup method so I could use them from the start, but only added them in when they're available in the wild. I didn't even evolve my Rhyperior into its final form until after I'd defeated the Pokémon League, despite having spare Protectors in other saves.
It actually made for a very rewarding save, as the disobedience up until badge 5 eroded all the advantages. Then, as the story ramped up and Team Galactic became more obviously dangerous, my now-harmonious team swatting aside all opponents seemed like my character focussing on what really matters and finding battling trainers inconvenient.