It all depends on your needs. For me, getting a Nucleus was an "easy" button that fit my system needs.
I bought a nice DAC and wanted to use it in my main system. I had also been considering moving to Roon. I found a used Nucleus at a very good price. It allowed me to use the DAC in my main system without adding another streaming device, and allowed me to use that DAC with Roon. The DAC isn’t "Roon Ready", but connecting it directly to the Nucleus made that a non-issue.
Using the Nucleus allowed me to copy my digitial files over to its hard drive and send them directly to the DAC instead of over my network and kept the Roon Core off my already somewhat bogged down computer.
It was the perfect solution for my needs. It might not be for yours.