These AMPscript functions provide a means for interacting with the Marketing Cloud SOAP API in the context of a microsite page, CloudPage or MobileConnect SMS message. While they are more verbose than the regular AMPscript functions, these API functions do provide some additional granularity of interaction with the platform.
It is helpful to be familiar with the SOAP API Objects and Methods, specifically the SOAP Envelopes in order to get the most out of these functions.
You might use these functions when you need to retrieve data with more advanced filter criteria than the Data Extension Lookup functions afford. You can also use these functions to interact with other Marketing Cloud objects that do not have a corresponding AMPscript function (for example, AccountUser, ListSubscriber, DataFolder, QueryDefinition, ContentArea, etc.).
NOTE: In order to utilize these functions, Web Services must be enabled in your Marketing Cloud account. These functions do not work in the context of an email.