it hasn't happened yet; however, we are in the process of making a FAQ/guide. Just currently with the maintenance coming up the GM's have been slightly busy with other more important things.
For now the answer is either given by players or you will be referred to the appropriate forum.
To mostly answer your question the benefits are as such:
Fishing:
You gain the opportunity to catch fish (obviously) which act as both a recovering agent for hp & sp, the type of fish caught depends on the type of recovery you will gain. You also have the opportunity (if you're lucky enough) to catch OCA and other various items/equips/etc..
Fishing starts two maps west of prontera.
Mining:
The biggest benefit of this is the ability to mine the various ores strewn throughout the game, instead of having to hunt them. The downside is it will make you overweight easily and is in a fairly hard location depending on your level (and class you start the quest with... I originally did it on priest not paying attention... bad mistake).
Mining starts at the Mine. (Take the warp from Alde)
If you ever have time to freely look around the forums all the info you need is
here
:edit: aki beat me