Your Trainer ID and Secret ID determine which 'spreads' - IV and nature combinations - are shiny. By RNGing it you can get shinies with top-quality sets, whereas normally shinies have mediocre stats.
If you just want flawless Pokemon, you don't need to do it.
If you want to get started RNGing, my advice is use a high-levelled, static legendary. My first - and to date only - RNG captures were Dialga and Palkia in Platinum. Both near-flawless Jolly. Ideally have access to Emerald so you can clone Master Balls and Pal Park them across. If you don't have Master Balls, a "one-under" Pokemon is strongly advised - a Pokemon with a speed slightly less (ideally 1 less) than the speed of the legendary if you hit your spread. If the one-under Pokemon attacks before the legendary, then you know you missed your spread and can immediately retry.
If you just want flawless Pokemon, you don't need to do it.
If you want to get started RNGing, my advice is use a high-levelled, static legendary. My first - and to date only - RNG captures were Dialga and Palkia in Platinum. Both near-flawless Jolly. Ideally have access to Emerald so you can clone Master Balls and Pal Park them across. If you don't have Master Balls, a "one-under" Pokemon is strongly advised - a Pokemon with a speed slightly less (ideally 1 less) than the speed of the legendary if you hit your spread. If the one-under Pokemon attacks before the legendary, then you know you missed your spread and can immediately retry.