It depends on your play style.

For adventuring classes, crafting is useful to give yourself new equipment while leveling. The dungeon drops are better but then you have to rely on running the dungeons repeatedly to get the drops.
For crafting/gathering classes, there are no equipment drops so the only way to get high quality equipment is to make it yourself or buy it from the market board (made by another player). The level 55 equipment is also not available from NPCs so it has to be crafted.

Post-50 the crafted adventuring gear is always behind what is available with tomestones (crafted 110 vs poetics 120/130 right now) but can give you a boost while earning enough tomestones for that gear. The main use for crafting at that point (for me) is making glamour prisms, making housing items, and repairs.
Glamour prisms - glamour is available once you hit 50 with an adventuring class. You need a separate prism for each item you want to glamour. The type of prism you need is based on the level and type of the gear image you want to project. The completed prisms usually sell anywhere from 5k-20k depending on the server. The recipes themselves are use easy level 25 components though, so it is easy to make them yourself as a crafter.
Housing items - like 90% of the items for houses are crafted. Some of them are ridiculously difficult too.
Repairs - if you have an appropriately leveled crafting class you can repair your gear whenever you want. It is very nice being able to repair gear in the middle of a dungeon.

If you get into crafting you are going to want either botanist, miner, or both just to gather the elemental shards you will need.
Fishing is awesome (I think) but doesn't really tie much into the other classes. There are relatively few uses for fish.