I've used these tools on-and-off an awful lot, and I decided last month to entirely stop using LLMs for programming (my one exception is if I'm stuck on a problem longer than 2-3 hours). I think there is little cost to not getting acquainted with these tools, but there is a heavy cognitive cost to offloading critical thinking work that I'm not willing to pay yet. Writing a design document is usually just a small part of the work. I tend to prototype and work within the code as a living document, and LLMs separate me from incurring the cost of incorrect decisions fully.
I will continue to use LLMs for my weird interests. I still use them to engage on spiritual questions since they just act as mirrors on my own thinking and there is no right answer (my side project this past year was looking through the Christian Gospels and some of the Nag Hammadi collection from a mystical / non-dual lens).