I used to catch most things by spamming Ultra Balls without focusing much on damage/status unless it was a high level. Legendaries were the main thing that might need repeated reloads - for those not familiar with the games, most legendaries are a one-shot deal; if you fail to catch them and either lose or defeat it, you can't try again without starting a new game, so everyone always saved before attempting to battle them so they could reload on failure. There are a few legendaries that are exceptions, which moved around and could be re-encountered if not caught, but they were in generation 2 and upwards.