I feel the same, it's not that clear-cut. I think it can serve to convey understanding, familiarity, and also safe space to share that particular thing without judgment (i.e. like saying "don't worry what I will think, I've been there"). That's why I also have the need to do it when listening to others and caring to make them more comfortable and trusting to share.
Of course, the difference is usually whether it is done more as a side-note while keeping focus on the first person, once or twice in that conversation - vs getting excited and shifting focus to own experience, continuing to expand and branch the retelling, or remembering 5 additional occasions when that happened...
I think it can generally be clear whether you care and are participating in the conversation by doing it, or being self-absorbed and not really wanting to hear and emphatize...
Also, that sounds like a quite difficult situation, and glad to hear that you had opportunity (at least at those occasions) to share and feel un-alone in it. I hope it gets better.
Of course, the difference is usually whether it is done more as a side-note while keeping focus on the first person, once or twice in that conversation - vs getting excited and shifting focus to own experience, continuing to expand and branch the retelling, or remembering 5 additional occasions when that happened...
I think it can generally be clear whether you care and are participating in the conversation by doing it, or being self-absorbed and not really wanting to hear and emphatize...
Also, that sounds like a quite difficult situation, and glad to hear that you had opportunity (at least at those occasions) to share and feel un-alone in it. I hope it gets better.