Actually filtering out large crud from the cooling system (27 micron element in the filter I mentioned above) IS a good idea. Rust, scale, etc circulating in the smaller passages of the engine, heater core, radiator, water pump, etc do not add to system longevity.
Mandatory-- or course not.
Part of how important it is is how religious one is about changing coolant, monitoring and adjusting coolant SCA level if the old generation coolant, etc.
Eliminating the filter was a COST SAVING ISSUE (read that bean counter, not engineer decision). The bean counters were correct-- very unlikely that eliminating the filter would result in failures during the warranty period.
Ex: 2003 Alpine 38FDDS