I don’t need neither $sth handle for reuse nor the placeholders to re-execute the code

Placeholders are not just beneficial for handle re-use. See eg. Re: What are placeholders in DBI, and why would I want to use them? and the related allusions in Databases made easy. Perhaps your data would otherwise have been incorrectly quoted or incorrectly escaped or be of the wrong type or be in an inadmissible format, etc. Use placeholders or be prepared to explain and justify precisely why you have chosen not to.