You can offload the simpler things, but struggling with the simpler things is how you build the skills to handle the more complex ones that you can't hand off.
If the simpler thing in question is a task you've already mastered, then you're not losing much by asking an LLM to help you with it. If it's not trivial to you though, then you're missing an opportunity to learn.
The biology of the human brain will not change as a result of these LLMs. We are imperfect and will tend to take the easiest route in most cases. Having an "all powerful" tool that can offload the important work of figuring out tough problems seems like it will lead to a society less capable in solving complex problems.
If the simpler thing in question is a task you've already mastered, then you're not losing much by asking an LLM to help you with it. If it's not trivial to you though, then you're missing an opportunity to learn.