B: Use the Patch function to modify records in complex situations. Such as, when you do updates that require no user interaction or use forms that span multiple screens.
CE: Context variables are scoped for Screen. They are great for passing values to a screen, much like parameters to a procedure in other languages. Can be referenced from only one screen.
Functions available for context variables:
UpdateContext
Navigate
Note:
Use the UpdateContext function to create a context variable, which temporarily holds a piece of information, such as the number of times the user has selected a button or the result of a data operation.
Context variables are also preserved when a user navigates between screens. You can use Navigate to set one or more context variables for the screen that the formula will display, which is the only way to set a context variable from outside the screen.
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-patch
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-navigate
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-updatecontext