Technical reasons for using the different length cages mech:
Rear mech’s are worked out by calculating the bikes capacity…
Capacity = (Biggest front ring – smallest front ring) + (biggest rear cog – smallest rear cog)
So assuming a 22 and 36 teeth front chainrings & a 11 – 32 cassette yours is:
(34-22) + (32-11) = 33T capacity.
Shimano XT rear mechs (for example):
SGS (long cage) 45T capacity.
GS (medium cage) 33T capacity.
Admitted these are old figures, check Shimano’s web site for latest capacity, max cog sizes etc
So a medium cage mech would be fine but if you had a 11-34 tooth cassette (capacity would be 35), if you avoid big front/large rear combinations you’ll get away with it..
That and being as it has a shorter cage it has less likely to catch stuff on the ground…