The Panthers have had some injury issues at linebacker in recent years so they're hoping David will be able to stay healthy in Carolina.
SB Nation's Panthers blog, Cat Scratch Reader, explains the pick:
Panthers HC Ron Rivera indicated early on he is looking for impact players on defense, in particular the front 7. We also have a big question mark as to whether LB Thomas Davis can achieve what has never been achieved to date in the NFL; to return to the field after a 3rd ACL surgery on the same knee. Even the best case scenario warrants an early selection for one of the key positions in the Panthers 4-3 base defense; the weakside LB. Lavonte David not only fills that role extremely well but he also rises to the NFL in a manner similar to the guy he will back up.
David played the 2011 college season around 225 lbs but has since bulked up to 233 lbs as measured at the combine. The added weight didn't affect his speed the slightest (4.56) and so, just like Davis he is being questioned as to whether he is a safety in the NFL. Like Davis, Lavonte will put on a little bulk and settle in at WLB whenever Davis is not able too, whether that is this fall or another season or two. In the meantime he will also be another boost to our special teams unit.
On the field David brings the speed to cover TE's out of the backfield, a talent sorely missing in 2011 without Davis or MLB Jon Beason. He shows a talent for penetrating the line and making tackles for losses both in short yardage and end runs. David has great football instincts, is physically strong and is a sure tackler, making him the kind of impact player Ron Rivera seeks from the WLB position.