Personally, no, but back in the days before formula that was the only option for alot of mums. My friends have done it. One was weaning & needed relief, so fed the friends baby. I was offered for the same reason, but I didn't feel comfortable with it.
My natural instinct with friends upset babies is to pick them up & put them to the breast if they cry. Any baby. But I wouldn't do it. It crosses boundaries for most.

Each to their own.