Non Catalogue : Does is it necessary to define the Non Catalogue Items into the Master Item and then

Hi ALL, I am a bit confuse in Non Catalogue Items ???
Is is necessary to define them into the Master Inventory Org and then assign Accordingly to specific IO'S. Actually question at the Time of raising the Non Catalogue Request we are un aware of the Item and we also dont have corresponding Information too so how do we call the item under the Non Catalogue Request ??