The longer cage take up more chain- so you can have a little tension in small/small and not be out of chain when in big-big.
Small point but it makes a difference if you are not a careful shifter.
I ran an 11-32 with my short cage 9000 this weekend. Works fine but I personally would not shift to the 32 when in the big ring. It makes it on the stand- I see nothing but trouble on the road.
Unless maybe you ran another link of chain. Then it would be sloppy in 11 cog on small ring- maybe even 12 cog.
I think the only difference will be idiot proof shifting (with 11-32) if you put the GS cage on.
With a short cage you must be careful enough not to go big-big, with a GS you don't have to worry about that.
What? Apparently some folks do not understand what the cage length on a derailleur does. The cage length, short or long, merely wraps up excess chain so it does not hang down under the chainstays when in the small-small combination. It is the CHAIN LENGTH and how the derailleur shifts that determines whether you can use the big-big combination. 50 chainring and 32 cog in this case. The chain has to be long enough to go around both big ring-big cog without yanking the derailleur off the post. Just in case by accident you shift into the big-big combination. You're not supposed to use big-big, but just in case. And the derailleur itself has to be able to get its upper pulley underneath the 32 cog. Some rear derailleurs are built so they can only get the upper pulley so low under the big cog. Derailleur design. You have no control over this. When in the 34 ring and 32 cog, the chain will be fairly tight so both short or long cages will wrap up plenty of chain and keep the chain taut under the chainstay. Shifting the rear derailleur to the 32 cog is 100% INDEPENDENT of what cage length is on the derailleur. Irrelevant!