You getting answers for two different things:
The first, firing a cap or two with no load is ensure that your nipple if free of oil and debri. The flame from the cap blows obstructions out of the flame path. This step is more important for traditional ML shooters, but is still a good idea for in-lines. I shoot a traditional gun, and always do this prior to loading when hunting. The patch is opitional - if there is a lot of oil in the barrel/nipple is can help absorb some of the excess oil.

The second issue, is some MLs seem to shoot differently with a clean vs. a fouled barrel. Most folks who deal with this will site there guns in with a fouled barrel, then fire a shot, to foul the barrel, before hunting. This way, any follow up shots will hit the same as the first shot. If you gun does this, you just need to know where your gun will hit when fired.

Hope this helps