Okay, I was making soup today, and it called for 3 cans of beans and a can of tomatoes. I wasn't sure of I should rinse the tomatoes or not (the can said they were in "tomato juice" which could be good for the broth), so I asked my grandma about it, and she was like, "no, don't rinse those" and in reply I said, "but rinse the beans, right??" and she said, "No, and you can use some water to get all the juice out." I already had rinsed and put in two cans, so I was thinking, okay, I'll try this with ONE can of beans. This was a poor cooking decision. My broth was muddy, too salty, and had the grainy feel of preserved beans. Still edible but not the best. Otherwise it was an amazing soup (but it made a ton and it's kind of difficult to get all those cans back on a bike).
Bottom line: Always rinse your beans, no matter what your grandma says!