Two sum solution - why dictionary

Hello,

I would like to ask about the solution to Two sums.
My idea is just to return i,j which goes trough for cycles as indices.

def two_sum(L, target):
    for i in range(len(L)):
        for j in range(i+1, len(L)-1):
            result = L[i] + L[j]
            if result == target:
                return [i, j]
    return -1

What I don't understand is why should we used a dictionary in the solution of this exercise.
Does it bring any benefit?
Thanks,
Best,
Maros J