Well, I would definitely say NO to your question. Having said that, it also depends upon your experience, market, and company. If you are a beginner, then focus on core FI/CO like G/L, AP, AR, CCA, IO and PCA, whereas, learn the business process and system flow for AM, CO-PA and Product costing, so that you can at least talk about it. To learn the latter, as a beginner, will be a humongous task and you would lose interest easily as they are integrated with other modules as well. And, most importantly, learn the business process behind every config you do. How is not as much important as Why. Even focus on the integration with SD and MM coz whatever they purchase your liability (AP), and whatever they sell your asset (AR). As a FICO consultant for last 2 and a half years, I would definitely recommend FI/CO if you have passion for accounting and internal controlling. You will be directly involved in designing the entire accounting system and providing the best solution for CFOs. Not a cake walk though. I am sure you wouldn't mind lot of sleepless nights coz the pay back is beyond imaginable.