When I bought my home, the fridge had a big ol burn spot on the side of it from the stove being right next to it lol. That’s probably what people may be referring to. I never use those two burners because of that despite getting a new stove and fridge since moving in just seeing that. Also the refrigerator sides will naturally get hot/warm as they expel heat from normal operations, so putting it next to something that is hot can be somewhat counterproductive for that too. Not going to cause it to overheat, but may not be the best position if you can help it. Kind of like how you wouldn’t want to put a heater positioned near your gaming PC if you want the best possible performance.

I know it can lower the lifespan of the fridge, but unsure if there’s more than that!