Re:
The difference is just the amount of chain they can wrap around it. So a long cage lets you use a wider range of gears.
Long cages are actually more common, or should be.
Weenies used the short cage though.
In the real world, both will run on 32 -12 cassettes , with 24-26-46 chainrings. As was common back in the day.
A short cage just gets floppier earlier on granny ring/small rings at the back.
Setup is the same.
If for some reason you like to live dangerously, you can set it up 'wrong' so you can run more granny gear ratios, but risk and will jam it in big/big or snap the chain.
That's up to you.