Newer players often wonder if Go skills on one board size are universal to any board size. What do you think? How would you describe it?
the biggest difference imo is the value/effect of influence.
On 9x9 there is no center to fight over, as the board is basically entirely corners, and all stones radiate some sort of influence over the entire board, even the third line “territory” moves. This makes a moyo generally a bad idea as basically any moves on the board an influence to assist an invasion, so all the influence is directly tied to the fighting that is likely to occur.
On 13x13 there is a center, but it’s only about 4x as big as a corner, which leads to focus on corner territory. As far as I can tell this makes influence as something that is useful for fighting a tad less valuable than 9x9, while still making influence with the intention of a moyo similarly bad, albeit better than 9x9.
On 19x19 however, the center is about 16 times bigger than the corner, making moyo moves much more viable, while influence for fights is even more localized than 13x. This means that influence is once again valuable, and that fighting is going to ensue, but on this board, fighting rarely means trying to kill outright, and not always trying to make it small as possible with endgame moves, but rather trying to see how you can use this group being unsettled to make some territory somewhere else.
I think mekriff’s good answer possibly understates the difference between 9x9 and 19x19.
At least at DDK level, 9x9 is all about fighting & tactics, whereas 19x19 is all about strategy and building.
The rules are the same, but they are different games. At DDK you can do quite well in 19x19 without really being able to read a fight, which is not true in 9x9. And you can be fine at 9x9 and totally lost on 19x19 - looking for a fight the whole time and building nothing in the process.