可読性

void fetch() {
  if(login) {
    if(admin) {
      // fetch something
    } else {
      log('Must login in your an account.');
    }
  } else {
      log('Must be an administrator.');
  }
}

void fetch() {
	// 早期リターン
	if (!login) {
		log('Must login in your account.');
	}

	if (admin) {
		// fetch something
	} else {
		log('Must be an administrator.');
	}
}

if (steps >= 10000 && caloriesBurned >= 500) {
  // Goal achieved
}

// 説明変数で条件の意味をわかりやすくする
final isDailyGoalAchieved = steps >= 10000 && caloriesBurned >= 500;

if (isDailyGoalAchieved) {
  // Goal achieved
}