That is the main and only use I have for a mandrel. It does help to hold and control the buffing. Once one gets some experience with buffing, buffing wood with wax brings out a great patina on some woods - for those who do not want the shine of CA.
Something that I learned early on when buffing (from Zac Higgins over at NVWoodwerks) was to make a tapered dowel type of tool that you can insert into one end of the blank while holding the other to buff the blanks. Some folks use a metal mandrel to hold them, but any metal will cause your buffing wheels to get very dirty (turn grey). That doesn't happen if your holder is made of wood - and holding the blanks without some kind of tool can be difficult as well - since you wind up buffing your fingers as well as the blanks.
I started out with the PSI lathe mounted buffing system, but went to a stand alone system after just a short while. I didn't like swapping my pen tooling out for the buffer on my lathe I guess. I wound up with a Rikon 8-inch slow speed buffer, but I replaced the 8-inch wheels with a 6-inch sewn cotton wheel (for use with the blue buffing compound) and a 6-inch loose flannel wheel for the other side. (Considering the linear velocity of the 8-inch wheels, I dropped the size to 6-inch to reduce the linear velocity to more closely match that I was using with the PSI lathe system. I'm very happy with the results and with the results I get on my pens.
I had a long tapered metal punch (old Craftsman) that is heavily chromed. It doesn’t do anything to the wheels and holds the blanks nicely. If and when the chrome wears out (hundreds so far) I’ll likely make a wooden one.