Originally we did home use by buying additional regular licenses. On a renewal about 4 years ago Symantec offered a sku for home use. those were a lot cheaper. On a renewal since then I was told that the home use license only had to be bought once. Makes some sense since support isn't included for them.
I STRONGLY encourage my users to get a security suite. I believe SEP's personal firewall isn't very usable for as a unmanaged product, and the user's home computer would be better off with a consumer suite. Often these are available free from their ISP or at a highly reduced cost if you check out the sales.
Contrary to what some others say, It hasn't been my experience that exporting a unmanaged client from SEPM results in license usage. You need a license for the home client to get the reputation info. So you'll want to create the install package from SEPM. That doesn't mean a unmanaged client will report in and be counted as a license.