Do you understand what parallel means? Most LLM responds in seconds, there is no parallel work for you to do there.
Or do you mean you are using long running agents to do tasks and then review those? I haven't seen such a workflow be productive so far.
I run through a really extensive planning step that generates technical architecture and iterative tasks. I then send an LLM along to implement each step, debugging, iterative, and verifying it's work. It's not uncommon for it to take a non-trivial amount of time to complete a step (5+ minutes).
Right now, I still need to intervene enough that I'm not actually doing a second coding project in parallel. I tend to focus on communication, documentation, and other artifacts that support the code I'm writing.
However, I am very close to hitting that point and occasionally do on easier tasks. There's a _very_ real tipping point in productivity when you have confidence that an LLM can accomplish a certain task without your intervention. You can start to do things legitimately in parallel when you're only really reviewing outputs and doing minor tweaks.