Though experiment:
One mount point, three HDD's. You write a file to /home, which HDD does it get written to?
In general you have one block device per mount point.
Ways around this limitation:
1)Use RAID for the 3+ HDDs, then they appear as one block device and can all be mounted to /home. RAID takes care of where data is written.
2)Mount separate users on /home to separate HDDs.
/home/skittle on /dev/sdb
/home/turkey3_scratch on /dev/sdc
/home/ijack on /dev/sdd