For players of the market, gathering professions are largely worthless as a skill because they can usually buy the mats and have higher profit by investing the saved time on other gold making operations. But, there is an exception. During the first ~4 days of an expansion the mats prices are usually obscenely high so they may want to try to make some gold making that way.
Speaking from personal experience (I actually attempted it during MoP's launch), it's not worth it unless your gold making is the absolute #1 priority in your WoW endeavors. For me it's fun and useful but I wouldn't put it above levelling and advancing a character. For that reason alone it might be best to keep levelling/advancing a character for the first few days.