Sometimes there are more than one WordPress installation is necessary, but your host might have limited MySQL Database allowance. Well the solution to that problem is having multiple WordPress installation in one database.
You must install WordPress manually in order for this to work. Most one click programs like Fantastic would not let you choose the prefix.
During the installation in your config.php phase, you want to change the prefix “wp_” in order to allow multiple installation. So it can be wpchris_ and the next one can be wpben_ you can use different prefix and use them to create as many installation as you need.
That is all you really need to do. This is also a security measure that you can take even if you don’t have to install multiple installation. By having a prefix, you are making the hacker work more to find out what is the SQL Address before he can hack.