Hi Fred,
Couple of reasons I would say are a) Re-usability and b) Easy maintenance.
a) re-usability:
If the calculation view you are trying to build is on some master data, then the same master data would be useful for different reporting object as well where you can reuse the same attribute views.
Like for example customer information can be used to analyse Sales as well as purchase information.
from re-usability perspective it would be better to create individual attribute views and use them calculation view.
b) Easy Maintenance:
for GUI based objects like attribute views,analytic views and calculations, you can easily check where used list by right click on it or if you open the object you will quickly come to know what tables has been used and how those are joined.
However if you directly use tables then to check the dependency you need to look at view OBJECT_DEPENDENCIES in SYS schema.
In my opinion the best practice would be if the solution is feasible using GUI modeling then go for it, if not then only create script based object.
Regards,
Venkat N.