Why is it required to delete Install folder after installation of PrestaShop?

The reason for deleting install folder is that it contains the PHP code that configured your store. So it might be very easy for anybody who knows it is there to rerun the install process with erroneous information and mess up your store.
Steps to remove Install Folder:
This is probably the quickest thing to do :

1. Open FTP of your server by entering username and password.
2. Find the install folder. It is nice and prominent, near the top, under the img folder.
3. Right-click on it and select Delete.

Without Install folder and installation files, No one can run the install process again.