There are some benefits to exping. You can obtain crystals, which can be sold or used for crafting. You can also get items that can be used in crafting. You can get items that you can use to finish quests to increase fame.

If a new person starts and takes 2 jobs (Main/Sub) up to 30 in a week, and then leeches them to 90 in a few days, he/she has no Gil, their mog house is at 50 and their gobbie bag is at 30. I hear a lot of complaining about storage space. This must be killer for those collecting seals and such.

In my opinion, exping helps gain fame, gil and experience.