When they become "cling ons"? I will go to great lengths to help a friend, even a stranger clearly in accidental need but then I move on. Or its clear they can help/ should help themselves. Is that your question?
I was caregiver to my aging parents until two years ago. My Mom went first, dementia ushered in her collapse. My Stepfather second, picked apart over years by Parkinsons.
I am fortunate to have been able to help them through this, this is a service which can know know no limits. There was no line. Now they are gone. I am free of a burden of duty. Had I done less the regret might consume me.
So yes, there are times when there's really no limit, within what is humanly possible. And there are those times when the comfort which comes from giving it your all, to look back and know that there was no line...
I'm going to have to leave that sentence hanging, incomplete.