There's a reason that classes in Final Fantasy are called "Jobs." A Job is something you do to maintain livelihood for yourself and/or your family.
DoW/DoM jobs are high risk and high reward. You go out and brave the elements with your sword and shield or cane or scepter, and triumph over adversity in the hopes of earning tons of gil or getting nice items either to help you kill bigger things for better rewards or to sell for a nice profit. You earn shards with every kill on top of your normal leve rewards, and generally have a great time of it. Sometimes, you travel in packs and offer your skills to others to get even bigger rewards in the form of SP gains or even better loot that it takes a party to wrest from the hands/claws/eyestalks of bigger and badder baddies. You come home with a sack of gil, backpacks laden with treasure, armor, weapons, baubles, etc... and trashed gear.
DoL jobs are low risk with medium reward. Mostly you wander around unscathed with your pickaxe/hatchet/rod looking for sweet looking trees/mountains/lakes to plunder. At the end of the day, you probably haven't had to face any mortal danger unless you've been drinking heavily and drive your own pick into your eye/play chainsaw vs arm/embed your lure hook in your ******. You come home with a bunch of shards, backpacks laden with raw materials you will be eager to sell your DoH buddies... and trashed gear.
DoH jobs are low risk with... wtf do you mean I have to pay for all these shards?!? So, if I want to do my job, I'm completely reliant on the others for materials and shards minus the paltry leve reward materials and maybe 100 shards if I do all 8 every 36 hours? Well, if I plan to get level 40+ in any given craft, it's going to cost me as much time or more than it took you to get there by slaying baddies or chopping/mining/fishing, but I have to somehow earn enough gil to buy all these mats to complete synths... I KNOW! I'll sell the things I make! So, let's see... to skill up to 10 where I can make decent stuff people might want, I'll need to just make these copper nuggets and turn them into copper squares, then turn those into copper toes. Phew. Ok, I bought 4 yellow copper ore from one of those miner guys for 250 each, and a fire crystal from that mage over there for 2500. Sweet, now I have 12 copper nuggets... why that's like 48 squares, which is 24 copper toes! Uh oh... every one of these square synths takes 6 earth shards. 72 earth shards coming up... that's another 15k down the drain, but man, I'm really levelling up like a boss here! Ok, time for toes... 24 synths using 1 wind shard and 5 more earth shards. Ok, 24 @ 300 and 120 @ 200... Dear god. Well, if I cut back to half a loaf of bread per day and drink water, I guess I can afford it. 31,200 gil later, I'm back in business! Ok, I have my 24 copper toes, I'm Rank 7 Armorer, and it only cost me 49,500 gil! So, to turn a profit, I need to sell these toes for at least 2063 gil each... My bazaar is up... WHY AREN'T PEOPLE BUYING FROM ME?!?!?
Hey, there's my Gladiator pal! Hey bud... you made rank 7 today? Awesome! You made how much gil today?!? Holy crap... Oh... your stuff got mangled in the process. That's too bad... you know, I can fix your armor now! How much? Bwa... Bwahaha... BWAAAAAHAHAHAHAHAHAHAHAHA! What's that? Oh, nothing... 10 gil sounds great! I know that Gorgano guy was gonna charge you like 20 times that for a shoddy job... I'm just glad I could help you, my good buddy, out of a jam. Say, do you have any shards or crystals you could help me out with? 200 gil each? Well... ok. You don't happen to need any fine quality Copper Toes, do you? No? Didn't think so.