@TanyaS58 Generally node level page config are set only if the data is shared across all the users in the application irrespective of the Access group of the user. They still need an access group because Pega needs a way to know which rules to use, even though there's no logged-in user at that point. Basically node-level uses for integration. 

Node-level data pages are shared, so they can't be editable or savable — to avoid chaos

Hope this helps.

@TanyaS58 Node level DP loads only once(based on time specified in Reload if older than refresh strategy) for all the requestors in the same node. Since it is shared between all the requestors it needs to be read only DP to have the data consistency. 

Pega executes the rules based on the context of the user's Access Group (defines the application context and security context). Multiple requestors can access the same Node DP in the same Node and these requestors can be using the different Access Groups. One may point to older application version, other may have different ARO, etc., But the purpose of the Node DP is to load only once for all the requestors in the same node. 

To load the Node DP irrespective of the context of user's Access group we need to specify the AG in the Node DP.

Hope I was able to answer your question.

Please feel free to check the below links as well.

https://support.pega.com/question/node-level-data-page

https://support.pega.com/question/why-we-need-access-group-node-level-data-page