When to use which code and how to think ?

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I have a confusion on handling these kind of questions.

For eg in the subsets question on Leetcode (https://leetcode.com/problems/subsets/). You can solve it using the approach which is similar to Knapsack problem and also using the general backtracking approach.
The major confusion I have is when to use which format.
Can somone help me with it?

class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        List<Integer> list = new ArrayList<>();
        findAllsubset(nums, nums.length, list, result);
        return result;
    }
    public void findAllsubset(int [] arr, int n, List<Integer> list, List<List<Integer>> result) {
        if(n == 0){
            result.add(new ArrayList<>(list));
            return;
        }
        findAllsubset(arr, n-1, list, result);
        list.add(arr[n-1]);
        findAllsubset(arr, n-1, list, result);
        list.remove(list.size()-1);
    }
}

The other way of solving is using the backtracking approach

class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        List<Integer> list = new ArrayList<>();
        findAllsubset(nums, 0, list, result);
        return result;
    }
    public void findAllsubset(int [] arr, int start, List<Integer> list, List<List<Integer>> result) {

            result.add(new ArrayList<>(list));
            for(int i=start;i<arr.length;i++) {
            list.add(arr[i]);
            findAllsubset(arr, i+1, list, result);
            list.remove(list.size()-1);
        }
    }
}

I usually get very much confused if I should use a for loop. It would be really helpful if someone could help me on how to approach these kind of problems.

PS - I am beginner to competitive programming. So, any guidance would be really helpful.

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