It gas several functions but with all of them they are maybe slight noticeable. I have a N21-5T and it has that hole in the crankschaft without the putty and that engine is running awesome.

The main reason is weight and the ease of production. They drill out the crankshaft and drill it a bit deeper to the front bearing. It saves weight and for adding the flow they put in the putty. There is a topic on ths forum of what people are using. Most of them are using Permatex high-temp RTV silicone or ThreeBond 1211 silicone liquid gasket.

But be aware the visable tuning like flowing, teardrops etc does not add much more power to an engine, it can make the engine run more smoother. Changing timings will make the huge improvements.