Electronics Newbie question concerning LEDs

When using many outputs with higher current, also the maximum ratings for output groups should be considered. For Cyclone II and III, 20 mA per pin is generally possible. You should avoid however to switch all pins simultaneously.

I generally agree with the opinion, that there are more economic options to drive a large number of LEDs than using a FPGA. If you want to add a few ten outputs to an existing system, it can be meaningful of course.

External, serial interfaced drivers for slow and medium speed signals, e.g. a LED matrix, have the basic advantage of simplifying signal routing. This can be a sufficient reason to use them, I think.