Hi,
The projection is used to apply filter inside a calculation view on a join of views or union of mutiple joins. There is no other way of applying filters inside a calculation view than applying a projection.
Whereas, aggregation is the default feature of calculation view. All the unions, joins or projections will finally merge into the aggregation box. Only the selected columns inside the aggregation will be visible in the calculation view output.
Regards,
Aditya Kashyap