HW = hardware errors, can also be usefull to keep your eyes on and figure out what's happening.
A perfect miner would be A:12342387463 R:0 HW:0
You can experiment in your .bat file with the Intensity to maximize your accepted value.
for example if you have 4 cards: 1 over-used, 2 used and 1 new, i would type
--scrypt pool.pool.com:3333 -u me.x -p x -I 12,16,16,18 --gpu-clock 750,800,800,900 --gpu-memory 1000,1100,1100,1200
or use MSI afterburner and in the setting unlock the sync and give every card it's own over clocking, although that's the same as the --GPU-clock/memory flags. doing them both is useless.
The goal would be to stabilize all cards at 80-84°C with highest possible accepted hashes. Every card has it's own behavior so you can do a lot of individual tweaks to extend their lifespan while maximizing their potential.