You will cookie cut faster with Chisel Chain, you will cut more wood faster with Semi-chisel as you don't/won't have to stop nearly as often to sharpen and it stays sharper longer, although it is slower/duller to begin with when compared to Chisel.
Think of Semi Chisel as a big round wave on a line graph with lower peaks and higher valleys. Where as, chisel is more peaky with higher highs and lower lows.
Or another way is semi-chisel is a man and chisel is a woman, it has its points, but its emotional, with associated highs and lows. The semi is just steady, always trying to work without the drama, headache and fuss.
Or chisel is faster and slower, Semi-chisel is in the middle always working.