If you're running it frequently, the Repla macOS app makes it easy to startup Jekyll so it automatically refreshes. After Repla is installed, you run it from the Jekyll blog's root directory and pass it the jekyll serve
command. For example:
repla server "bundle exec jekyll serve --watch --drafts" -r "...done"
Repla will be configured to refresh each time ...done
is printed in the console, which Jekyll prints when it finishes compiling your site.
Repla runs the Jekyll server process in a split below a browser split showing your site:

After Jekyll is running in Repla, you can also save the configuration to a file with ⌘S
, shut it down by closing the window, and run it again just by double-clicking the file. In other words, you can start your Jekyll blog again next time just by opening the file, without involving the terminal at all.
Disclosure: I maintain the Repla app.