We are upgrading our SagePay protocol from v2.23 to 3.0 to support surcharge fees. In v3.0 transaction registration post there are CreateToken and StoreToken which was not in the earlier version. What is the reason for create and store tokens? I went through the document but couldn't find a clue.
I believe this is related to their token system, allowing you to store and send card details as a token. If you don't use their token system you don't need to worry about it.
Sage Pay have destroyed their content recently so it's hard to find anything, here's a quick article on their token system - http://www.metakinetic.com/blog/2013/09/sage-pays-token-system-and-advancements-in-payment-gateways/