thought forms is the name our religious and occult leadership attribute to the angelic/demonic/entity structures that are referred to in their sacred texts
in my own discussions with both religious and occult they both tell me that how and why thought forms are invoked is a matter of their tradition as in:
you need to believe what they believe to understand why they utilize them
to a non believer there exists no effect or purpose

the requirement to believe the traditional beliefs to experience thought form effects may explain the diverse manifestation of thought forms evoked as it appears that each sect within a belief possess, by tradition of unique invocation , thought forms structured to express their unique belief, often with a broad structure of similar beliefs

the purpose appears to be possession as in:
the point of evoking the thought form is to be possessed by it`s enhancing information energy
this is carried out within strict ritualized ceremony perfected over generations of practice with the purpose to maximize the possession effect whilst safeguarding the emotional state of the possessed and safeguarding that the enhanced informational effect is focused on the agreed purpose of the invocation/possession

how and why this tradition of masking enhanced field effect, mostly formed via geometric shapes construction (sacred geometry), with a thought form/entity arose , i dont know