The venture benefit of combat retainers is that you can send them on one hour ventures to obtain specific monster parts. Skins, hairs, meats, bones, etc. There are a specific few of these that only drop from monsters inside of dungeons, which means the only way to get them yourself is to go into the dungeon syncked and hope the stuff drops to you. This is time consuming and the expected yield per run is quite low because other people have an equal chance of getting the drops. However, once you have a combat retainer at the appropriate level, you can specify, "I want you to bring back this item." You will then be guaranteed 10 of that item while you go do something more fun for an hour.