DIY is alot cheaper (only yeast and sugar), and you can't really overdose w/ CO2. Those are pretty much the only advantages of DIY vs pressurized systems.
Presurized systems will run around US$150-$200, but then you don't have to redo the solution every week, you can control exactly how much CO2 is going into the aquarium, and you can turn it off at night.
This is crucial becuase CO2 is part of the aquarium's plant nutrient balance that when disrupted gives rise to algae and poor plant growth.
It's alot easier to have a good planted tank setup with pressurized CO2, but if you're new or not that serious but would like to see the benefit of having a CO2 system, then go DIY.