There a number of theories/reasons Coples would be a nice signing for the Panthers. It's clear he would benefit from moving back into a 4-3 defense as a DE. As pointed out by Bill Voth be could also provide some insurance in case Charles Johnson refuses to take a pay cut:
What to Know About Panthers' Interest in Quinton Coples -
The Panthers need pass rushers. So signing Coples would allow Gettleman to check that box. And, no, that doesn't mean he'd be the only guy added. Carolina could look at other free agents and this draft is deepest on the defensive line.