It depends on what would the Pokédex contain.
If for each pokemon and each stat, we could see the amount of EVs gained by defeating a poke , e.g., if you defeat an Alakazam you gain +3 EV points in Sp. Att. , that would be a lot more easier for EV trainers to target the pokemon they need to train with.
Same goes for number of steps required to hatch an egg, egg moves, catch rate, the most adequate Hidden power attack for each Pokemon (e.g. Kingdra needs an electric hidden power).
The list is long but it would be a rewarding effort to build a perfect pokédex.