>>12189837Some trainers use their trainer cards to randomize their starter.
Like for gen 4 1-2-3 would be Turtwig, 4-5-6 Piplup and 7-8-9 Chimchar.
I personally never do this, because I normally go for the type advantage against the first gyms, or the complete opposite if I want to make it harder for myself.
It's totally optional, but as you can see, some people live by that rule like it's written in stone.