Temporary folders have a very important meaning: they provide a place to store files for opened applications. If you delete those files while the applications are opened, then you might have issues with the content currently opened. Firstly, close all the applications and then clean the temporary files.
Additionally, use CCLeaner to clean the files automatically to avoid breaking something: https://www.piriform.com/ccleaner/download
CCleaner is configured to automatically delete safe files.