All the data movement shouldn't even be a blip on your CPU usage. I think I get about 0% to 0.7% CPU usage on cgminer on a low-end Celeron.
If you're getting high CPU usage then something is wrong. Make sure "gen=0" is in the helixcoin.conf file. If you're on Linux make sure it's using the libOpenCL from the fglrx install and not the broken one from the AMD APP SDK (this might apply to Windows also, I have no idea). The broken SDK libopencl causes an irq storm.
That was an oversimplification, yes
Mind you, Sha3 is different from scrypt and i can confirm that the cpu usage is from the sha3 cgminer and not a wallet with setgenerate turned on.
I couldnt tell you exactly why sha3 uses cpu like it does, but there are no negative impacts observed by the dev team, so we quite like the algorithm