Do you know the meaning behind the saying of "If you need anything, just let me know"?

I've encountered some people who had said that to me...saying like "If you need anything, just let me know."

However, so far...I realized that it's not exactly 'anything' or like they will be there when I asked them.

I mean like...what are they trying to say when they said that, or it's just about "letting them know" because they never said that they will give it to me.