6. Why is it less-advisedly to use POST for creation and PUT for updating?

Hi! In the training part 6 "Implementing POST, PUT and DELETE with Fastify (4)",
It says:

Typically a service would either use POST or PUT for both creation and updates, or sometimes less-advisedly, POST for creation and PUT for updates.

I always have worked in projects where they use the POST for creation and PUT for updates. Why would it be better to use POST or PUT for both operations?

Thanks in advance