The Rishonim highlight the connection between korban pesach and matzah and suggest (as an asmachta b'alma - not a real limud) that matzah should ideally be baked on erev pesach when the korban pesach was offered. Other Rishonim reject this idea. While baking bo bayom offers the hiddur of fresher (and tastier) matzah, baking earlier has a halachic advantage in that before the time of issur chameitz set in, chameitz can be bateil. Therefore, waiting until the last minute carries with it the danger of not having bittul to fall back on in case of error.
I have yet to understand why some people try to bake their own matzah. The mitzva is eating not baking. The people who bake all day can probably do a better and faster job than I could.