Never heard that advice, and I had no idea why that would be best.
I just googled it and this is what I found: “The best way to crack an egg is on a flat surface so that the membrane stays intact, allowing the small shell fragments to stick to it without mixing with the rest of the egg. Many chefs also crack their eggs into separate bowls since it’s easier to find bits of shell in a translucent raw egg than in a floury batter.”
I always did it on the side of the bowl, as this was what my grandmother and mother did. Sometimes I get a piece of shell in the bowl, and then I would of course take it out. I may start doing it on a flat surface from now on, as per the advice by the pros.