Don't forget what Karen said!
"Strong Pokémon. Weak Pokémon. That is only the selfish perception of people. Truly skilled trainers should try to win with their favorites. I like your style. You understand what's important. Go on--the Champion is waiting."
Hmm...I really like that quote! When I started getting involved in Pokemon (in Gen. 3), I just played for the fun of it, battling through the Pokemon League. I just caught Pokemon to have 'em; regarding natures, either I just caught the Pokemon as is or determined the nature based on its appearance. With "EV training", I just gave my Pkmn 10 of each vitamin, then I just trained them to Lv. 100. I figured once I maxed out on vitamins and training, my Pkmn were as strong as they could be. But then I learned the true extents of IVs, EVs, and nature choosing.
I'm sorta okay with "Engineering" for good IVs and natures , but the game gets less fun, since you don't really meet Pkmn by 'fate' (taking 'em as is) but by engineering (only accepting Pkmn that fit certain parameters). For example, if neglecting a Slaking's Atk is considered a "bad decision", that means any Slaking with an Attack-hindering nature would never be chosen for competitiveness, only by 'fate' if you take what you get (which happened to be an Atk-deficient Slaking). If you equate it to real life, it'd mean that even if you try your absolute best at something (like a contest), if you don't fit certain parameters, you'll never win the contest unless there's a fluke/lucky break that occurs in judging that just
happens to allow you to win.
This is why I just
hate it when fully-trained terrible IVs Pokemon face off against fully-trained max IVs, because the bad-IV Pkmn have THE lowest chance ever of winning. These bad-IV Pkmn need battles to be drawn out to either inflict sufficient damage, freeze/paralyze the foe consistently for easy damage, or allowing Toxic or Roar/Spikes to take their full effects (ignoring EVs and movesets, which are up to personal decisions).
Anyway, trying to stay on topic, just playing through the game to become the Pkmn League Champion, catch all of the Pokemon, and complete the sidequests seem enough reason to play the game just for fun. The concepts of IVs and EVs have the
potential to add even
more fun, if you like competition or just wanna get through the Battle Tower!
With the concept of favorites, sure, I'll probably have 1 or 2 teams full of favorites when battling. But to add more variety, I'll usually mix around faves and non-faves in my team, regardless of tiers, stats, whatever. It makes the game a bit more 'fun' when battling with other ppl, because since your team is unpredictable, you always have the 'element of surprise' and you're always in for a surprise! You have 493 different possibilities for a single foe, and 14,357,588,953,446,649 different possibilities for someone's party (hopefully I did the math right for that permutation/combination!)
Basically, in the end, Pokemon is an awesome and fun RPG that everyone can get enjoyment from, regardless of personal training methods, battle or collection preferences.
*Sorry for post length and/or if I veered off-topic!