A really short version of it is that you don't need an agent if you have a well-defined solution that can be implemented in advance (e.g. the 'patterns' in this article). Programmers often work on problems that have programmatic solutions and then the advice is totally correct: reach for simpler more reliable solutions. In the future AIs will probably be smart enough to just brute force any problem, but for now this is adding unneeded complexity.

I suspect a reason so many people are excited about agents is they are used to "chat assistants" as the primary purpose of LLMs, which is also the ideal use case for agents. The solution space in chat assistants is not defined in advance, and more complex interactions do get value from agents. For example, "find my next free Friday night and send a text to Bob asking if he's free to hang out" could theoretically be programmatically solved, but then you'd need to solve for every possible interaction with the assistant; there are a nearly unlimited number of ways of interfacing with an assistant, so agents are a great solution.

Works great when you can verify the response quicker than it would take to just do yourself. Personally I have a hard ass time trusting it without verifying.