TOGAF is is useful in some ways. Indeed many ways, especially the ADM, and the use of its techniques to consider transitions to target, structuring multiple competing or collaborating concerns. It also gives you a high-level nonprescriptive, methodology, tools, techniques, and resources, as well as reference architecture and styles to base your work on. However you truly need to understand enterprise architecture to make the best of it. TOGAF is the last of four levels in the EA chain (most specific) and the principles and abstract reasoning tools required of enterprise architects comes before that. So I'd argue understand those in detail first, then look at certification. After all, don't forget to get is only one part of the OpenCA certification for a reason. It's not enough just to get together that's like having a Microsoft certification, without understanding Data structures and algorithms.