Rare Candies!

[Starry Windy]

It depends. I used to use Rare Candy on any chance when I get it in the past, but lately I've decided to give some Rare Candies only when I know I have maxed out my Pokémon's stats because I'm not sure if my Pokémon will raise its EVs when the level is already maxed up.

 

[tokyodrift]

When I was younger, I used them right away, that was until I actually learned the side effects of using them. I usually wait until the end of the game before I go into the Elite Four, since that's when I tend to go through my bag and use things I've had the whole journey that I don't plan on selling for extra PokeDollars anyway. Although I may use them during the journey only for getting say a specific move a bit earlier than I anticipated.

 

[Azelfino]

I usually use them at the end of the game to get a few levels in before challenging the champ!