Is there any harm in using NPM and Yarn in the same project?

Although a few commenters here say its ok to mix both yarn and npm on the same project, after using yarn and npm and then yarn again, this is what yarn has to say about it:

warning package-lock.json found. Your project contains lock files generated by tools
other than Yarn. It is advised not to mix package managers in order to avoid resolution 
inconsistencies caused by unsynchronized lock files. To clear this warning, remove
package-lock.json.

Since to me it is not any harm to using both them into one project.

I use npm and yarn (50/50) in dev environment. But on ci/di i use only yarn because it is faster, and i reduce build minutes thanks yarn.

Also they both create different .lock file names.