JJT of DMN (sub req) writes an interesting article explaining why Julius Jones runs better with a lead fullback as opposed to running from a TE set, the formation the Cowboys will use as their base this season. Jones himself believes a fullback clears out his running lanes much better.
"I know he's going to get one of the linebackers, and on a lot of the power runs, I feel more comfortable with the fullback in there."
I definitely agree with JJT that running backs like Jones need a fullback as opposed to TE's blocking for them. Just look at Emmitt, I truly don't think that he would be the all time rushing king without Moose Johnston as his lead blocker. I don't think Shawn Alexander wins the rushing title without Mack Strong. Running backs need a fullback to get past the line of scrimmage and thats where JJ had his problems last season.
Two tight ends bring balance to the offensive line, but it also tends to bring the linebackers and safeties closer to the line of scrimmage because it's usually viewed as a running scheme, thus congesting the field.
Parcells is using this scheme because it will open up our passing game and create severe problems for defenses, but I wonder how great JJ could become if he had a true lead blocker like Moose. I guess we might never know, at least until Parcells retires.