Why is the 'Regarding' field not a *Required* field by default? Am I missing something?

Hi all,

On any activity (e.g. Phone call, Task) why is the 'Regarding' field not a required field... ? You can leave it blank. 

Is there a basic reason I'm missing why you wouldn't want to force users to set a 'Regarding'?

Is there a drawback if I make it a required field for our organisation? I want to always have any activity record created put against something, not to be in no mans land.

Thanks