It's the why of the caseload that matters. Maybe ten years ago I started yearning for the chance to talk to fifteen-year-old me. Tell me it was all going to work out, tell me that the problems I was dealing with resolved okay, tell me that despite it all I fuckin' made it. It took me another eight years to realize that every orphan I'd taken under my wing as Reddit/Hubski's Father Confessor wasn't benefiting from my altruism, they were serving as proxies for my teenaged self. Which is not to say they didn't benefit. I doubt these relationships would exist if they weren't mutually beneficial. But the benefit to myself was obscured in a heavy blanket of adolescent fog-of-war. Explaining to others allows you to clarify your ideas for yourself. Tending to others can be a form of self-care. There are probably social workers who aren't emotional basket cases but I haven't met them; ultimately I have an easier time caring for others because their value is self-evident while my own well-being is near zero.
I don't quite understand the last sentence. Do you mean that you have an easier time caring for others when you are feeling shaky about yourself -- because what you are saying to them or helping them with helps strengthen you -- if that's it, then, yes, I see that. I also agree that we do get something out of the friendships that seem like work. On some days, that person might be just the one to get us out on a walk.