Just to let you know, which most others do, its
https://www.serebii.net, or just Serebii.
And stopping Pokémon evolving had certain advantages. EXP Points are not one of them, they grow just as quickly, only the Base Stats are increased.
Basically, some lower form Pokémon learn moves at a lower level than their evolved forms, or moves that the later stages will never learn, such as the Hoenn starters (Treecko = Giga Drain, Torchic = Flamethrower, Mudkip = Hydro Pump). However, this stops the evolved forms learning other moves, such as with Torchic, if you let it learn Flamethrower, Blaziken will never learn Blaze Kick (without a Heart Scale, but thats another matter). Its all about working out when to evolve them to get their best moves.
Pokémon that evolve via Elemental Stone generally have 'Maturity Levels'. This means the last level that it will learn any move, as the evolved form normally learns no additional moves other than 4 original moves. Normally, its best to wait until this level to evolve, to get the best moves, and then increase the stats via evolution.
Some, however, of these, are different. Such as Exeggutor, who will never learn Stomp, unless you evolve him early, which stops Exeggcute learning other, and moreso better moves. And yet again, more awkward learners, such as the Kanto Eeveelutions, who will learn many move after Elemantal Stone evolution, just mainly learning moves associated to their types. Eevee will learn Normal type move mainly, whilst Vaporeon will learn Hydro Pump, Jolteon will learn Thunder and Flareon will learn Flamethrower (I think).
Basicaly, what Im trying to say is that evolving all Pokémon will happen, no point in having a level 100 Magikarp, ey? Just
when it happens is entirely down to you. Use guides, or sites for advice, work out what moves you will want your Pokémon to learn through level-up, then evolve it accordingly. Hope it helps.