Are agent frameworks THAT useful?

I don’t mean to be provocative or teasing; I’m genuinely trying to understand the advantages and disadvantages of using AI agent frameworks (such as LangChain, Crew AI, etc.) versus simply implementing an agent using plain, “vanilla” code.

From what I’ve seen:

• These frameworks expose a common interface to AI models, making it (possibly) easier to coordinate or communicate among them.
• They provide built-in tools for tasks like prompt engineering or integrating with vector databases.
• Ideally, they improve the reusability of core building blocks.

On the other hand, I don’t see a clear winner among the many available frameworks, and the landscape is evolving very rapidly. As a result, choosing a framework today—even if it might save me some time (and that’s already a big “if”)—could lead to significant rework or updates in the near future.

As I mentioned, I’m simply trying to learn. My company has asked me to decide in the coming week whether to go with plain code or an AI agent framework, and I’m looking for informed opinions.