I got reply from master Saaya:

"hey man,
well i asked foxconn to include those heatsinks so you can glue them onto any chips you want to cool on the board. the sas chip for example gets a bit hot, and so does the pata/esata jmicron chip.

they are fine for normal operation, even in a badly ventilated case, but i personally would like to add heatsinks to it to cool them and i know many people would."

Now we know!