You shouldn't delete that directory.  If I remember correctly there are services that run in the background that regularly check those directories for background installation.  I do not immediately remember if those services are running or not on default installs, or if there is proper error handling upon the directories not being found.  However, when you upgrade your DNN portal, the directory will be recreated again.

However, I just remembered the most important thing...  Your install config, wizard, under contruction, and install logic is all contained there.  The upgrade packages may not include all of those files. 

Basically, I would suggest that you not delete it.

Ok i understand now that its a bad idea to delete the folder but what is stopping someone to go to that folder and run the install wizard?