Sorry for the newbie question, this is for my tow rig

I'm getting ready to pull the trans on my '01 2500HD all data says to use a torque converter holder. Is it really necessary? What exactly does it do?

I would assume its just a safety precaution. In the event that the tranny was tilted into an extreme forward position, the "holder" will keep it in place. You can take a piece of flat steel, say 3/16 by 2 inch by about 8 inches long, and put a little bend in the middle and drill a hole in one end. With that and a long bolt through a bellhousing bolt hole will get you a cheap holder. Or you could just be careful and not drop the sumbitch. Ive pulled all kinds of transmissions and never needed one.