Sometimes i like to jj describe before writing any code. It helps with mental clarity what i intend on writing or helps if i have to run away mid coding session (description will show in log so i can find it again)
In this scenario I'd instead jj new at the end, after im finished and ready to move on to the next thing.
You can then also just use `jj commit`. It will see the existing commit message and just move to a new clean revision.