This function allows you to preserve a list of attributes when building a renderer only cache. The UsageContext will be either aUNiagaraSystemor aUNiagaraEmitterand can be used to scope your variables accordingly. For example, if you were to require 'Particles.MyAttribute' in order to process the cache results you would need to convert this into 'MyEmitter.Particles.MyAttribute' by checking the UsageContext is aUNiagaraEmitterand then creating the variable from the unique name.