It is a good idea, but he didn't seem like the remote logs server type (-: I could be wrong.
Seriously, 99% of people who would put a regular HD in a PFsense box would just do a full install on that HD and be done with it.
Yes, that is fine if you use pfSense just as a simple firewall and router, but if someone uses services for penetration prevention like snort, squid+squidguard, HAVP and others, a huge logging partition is needed to figure out intrusion detection. Mere a simple firewall and router can be run from a floppy disk, still, but pfSense I guess has a larger scope. Just my two cents.