I keep my /home on the SSD, but some directories under my user(s) are symbolic linked to /data disk. Like ~/Downloads, ~/Dropbox, ~/VirtualBox VM's, etc...
Because then all the cache directories of the user can be accessed quickly, and the 'data'-directories can't fill up the root suddenly. For example when you create a VM in Virtual box with 64GB disk for a test, suddenly the disk might be full.
Due to reinstalling my os every 6 months (to have a clean system and to learn), I started writing some basic bash scripts, that in the end, I just run command by command anyway, but it gives me a lead and I put reminders. All my favourite apt-get installs are in there, fixes, tricks and my directory creation. Following is a part of it
##after your hdd is mounted on /data let's say
# remind adjust /etc/fstab
MEMEME=$(whoami)
MYSECONDHOME=/data/home/${MEMEME}
sudo mkdir -p ${MYSECONDHOME}
sudo chown ${MEMEME}:${MEMEME} ${MYSECONDHOME}
cd ~/
mv Downloads ${MYSECONDHOME}
ln -s ${MYSECONDHOME}/Downloads ~/Downloads
mv Documents ${MYSECONDHOME}
ln -s ${MYSECONDHOME}/Documents ~/Documents
dropbox stop; sleep 5
mv ./Dropbox ${MYSECONDHOME}
ln -s ${MYSECONDHOME}/Dropbox ~/Dropbox
dropbox start
##... and so on for others
##... remind to stop services before moving their directory