JS and CSS Cache files

How long do these Cache files exist before they are deleted or refreshed by Dolphin?

I am not totally sure of what I am saying and maybe I am wrong because I am not a Cache lover. But I think Dolphin does not delete them automatically. If you have them enabled, then you should delete them from your admin panel every once in a while. But I repeat, I could be wrong here.

This is exactly what I wanted to know.  I agree with caching not being always optimal but in the situation I am in I need them to persist (directory security limitations). 

Thank you very much!

 I understand, but please wait also the answer of someone more experienced in this than me.

I do know the chache system very well..so I repeat, I could be wrong.