You save a ton of time but you need to have more people in the group to bring the average level down. Typically the path for mage boosters is as follows:

8-16 RFC
16-21 WC
21-40 SM
40-50 Mara

Either watch some videos about how to do the above dungeons in one pull, or you can farm on your mage while getting boosted by someone else if that's not your thing.