Rebooting (Actually just restarting the search service) will clear only old, committed DAT files in those folders for a single server setup. If you have a DAG, the .DAT files from the other server will be replicated from the other server. If you want to clear those files in a DAG, you need to reboot both servers at the same time, I believe. That said, I've never seen any reason at all to clear them. If you don't have enough space for them and your database, start looking for more storage if you can.
Hello Plafond412, Thank you for your question.
The problem here is that in the question you referenced there's no "DAG" configuration or specified anywhere, or even multiple servers so I assume that is a single database within a single server. So this "solution" is not viable in your scenario.
Now
here's a more accurate answer related to your question
https://www.experts-exchange.com/questions/29111328/Is-it-safe-to-delete-old-Exchange-2013-content-index-files.html