Nicolas Cole says working on two projects at once guarantees both will be mediocre. Pick one and go all in. The only exception: if you're just writing for yourself with no goals beyond expressing what's on your mind.
Chapters
I am such a big believer in not trying to build two things at once. If your goal is, "Cole, I don't have any external goals. It's not about making money. It's not about achieving any sort of external result. I just want to write what I want to write about," then by all means, have two newsletters and write what you want to write about. But I have these two different topics, kind of like trying to chase two squirrels at once, and time spent on one means time not spent on the other. And that feeling, that opportunity cost, is what happens when you try and do two things at the same time. My advice to you would be pick one and focus 100% of your time on making one of them really great rather than 50% of your time making them both mediocre.