o boy. can of worms here.... BUT....
shorter arms give you a narrower power band. it's harder to stay "on top" of a given gear. that said, they're theoretically easier to achieve maxium steady-state power with, all things being equal. depending on your muscle fiber composition and general phsyiology this may suit you or it may not. if you like to shift, it won't matter as much, but WILL be noticeable if you're sensitive and/or torque-limited. if you're running a wide ratio (cough SRAM 1x) cassette and a big chainring that exacerbates those gaps, you may find the shorter crank arms a bit uncomfortable on undulating terrain.
there are advantages to them like ground clearance & less shear force on the knees, and disadvantages like raising your CoG and profile & reducing your maximum available instantaneous torque (in addition to what's mentioned above in the first line).
Discuss light weight issues concerning road bikes & parts.