There's also a huge plus.
They can block as well as run and catch.
Finding a back that can pick up a blitz package out of college is becoming a rarity. Carolina general manager Dave Gettleman believes that's a major reason no back was taken in the first round of the 2013 draft and only 10 have been taken in the first round over the past five years.
None, by the way, are projected to go in the first round in the May 8 draft.
By comparison, there were nine defensive linemen (tackle or end) and eight offensive linemen (tackle or guard) taken in the first round of the 2013 draft alone.
"The typical NFL run game is very different from the college run game, so there's an adjustment for those guys,'' Gettleman said. "The position has become deemphasized at the college level. . . . Blitz pickup is a huge issue. It's big.''
As a result, rookie backs are having trouble staying on the field. For example, Denver was high on second-round pick Montee Ball last season. Because veteran Knowshon Moreno was better at protecting quarterback Peyton Manning as well as the ball, he got the bulk of the carries.
"So you take a running back in the first round, he better be a three-down guy right now and there can't be any question in your mind that he can figure out the blitz stuff, because it's a real problem,'' Gettleman reiterated. "It's a real issue.''
Gettleman said the number of backs ready to handle an NFL blitz pickup package today is "rare.''
"They really are,'' he said. "There are some guys you can watch 10 tapes on and they never pick up the blitz. They're gone.''
There's another factor in the decline of first-round picks going to running backs. Teams expect their first-round picks to come in and be immediate contributors. The average season production out of the 10 backs taken in the first round since 2009 is 638.6 yards rushing and 5.1 touchdowns; 281.2 yards receiving and 0.8 touchdowns.
To put that in perspective, 32 backs had 650 or more yards rushing last season. More perspective, Carolina quarterback Cam Newton is averaging 677.3 yards rushing during his first three seasons.
Williams had had 843 yards rushing for Carolina last season.
Only Tampa Bay's Doug Martin, the 31st player selected in 2012, has surpassed 1,000 yards rushing as a rookie since '09. He had 1,454 yards and 11 touchdowns.
So while it's easy to gripe that Williams ($6 million), Stewart ($4,585,000) and Tolbert ($3,350,000) have the Panthers strapped under the cap, there are benefits to having them.
Their abilities to pick up blitz packages last season helped protect Newton and make him more proficient as a passer. Their skills as a runner and receiver helped make Carolina one of the top ball-control teams in the league.
Having them also has allowed 2013 sixth-round pick Kenjon Barner to develop pass blocking skills he didn't have at the University of Oregon.
Williams, Stewart and Tolbert may be expensive, but there's an upside when you consider what the Panthers want to do offensively. The alternative potentially is relying on a rookie.
Let's look at backs taken in the first round of the past five seasons and what they did in their first season:
Trent Richardson, Alabama, No. 3 overall to Cleveland -- Rushed for 563 yards and three touchdowns; caught 35 passes for 316 yards and one touchdown.
Doug Martin, Boise State, No. 31 overall to Tampa Bay -- Rushed for 1,454 yards and 11 touchdowns; caught 49 passes for 472 yards and one touchdown.
Mark Ingram, Alabama, No. 28 overall to New Orleans -- (Heisman Trophy winner) Rushed for 474 yards and five touchdowns; caught 11 passes for 46 yards and no touchdowns.
C.J. Spiller, Clemson, No. 9 overall to Buffalo -- Rushed for 283 yards and no touchdowns; caught 24 passes for 157 yards and one touchdown.
Ryan Matthews, Fresno State, No. 12 overall to San Diego -- Rushed for 678 yards and seven touchdowns; caught 22 passes for 145 yards and no touchdowns.
Jahvid Bset, California, No. 30 overall to Detroit -- Rushed for 555 yards and four touchdowns; caught 58 passes for 487 yards and two touchdowns.
Knowshon Moreno, Georgia, No. 12 overall to Denver -- Rushed for 947 yards and seven touchdowns; caught 28 passes for 213 yards and two touchdowns.
Donald Brown, Connecticut, No. 27 overall to Indianapolis -- Rushed for 281 yards and three touchdowns; caught 11 passes for 169 yards and no touchdowns.
Chris "Beanie'' Wells, Ohio State, No. 31 overall to Arizona -- Rushed for 793 yards and seven touchdowns; caught 12 passes for 143 yards and no touchdowns.