Separate server licences?

Hi I'm considering to start using Whm/cPanel but I'm a little confused on one issue. To run my website and WHMCS on its own server with its own cPanel and then provision my customers websites on their own server would I have to buy 2 Licences i.e. a solo for the business and say a Pro for the customers server or can you allocate cPanels to any server you run?