You say you have a Procedure (in writing I assume), some one must have put some thought and effort in to the Procedure and came up with a good reason for the preheat. That person may know more about what the material will be use for, exposed to or the kind of stress it will see.
Preheat is sometimes used to reduce thermal stresses also, and you say you are working with a forged material. There maybe concern that some yelding may take place from uneven thermal growth.
If you were just wacking the end off a piece of Cr. Mo. pipe I couldnt agree more, but a forging may be another story.