rules concerning materialised views and views

Hi, I found that it is technically possible to create views which use materialized views in their definition .. which on their turn were already looking at data from views (other views). There seem to be no technical limits enforced here, neither to the level you can go deep in such structures ...

... and also to the fact that views use materialized views (instead of tables only, or other data sources excluding MV's),

and the other way round: materialised views looking at views (instead of tables only, or other data sources excluding views).

All of this combined, what prevents from creating complex setups ? Or, stated differently: unnecessary complex setups.