Pros
Good discount, though products in store are marked up so high that the employee discount almost brings the prices close to those found online. Certain products carry a commission, though none of the ones you are pressured to sell.
Cons
If you have a conscience, its hard to load customers up on hundreds of dollars of unnecessary supplements that will have little effect on their health goals, its a requirement if you want to keep your job. The commission system is set up as such that the employees that run the "best numbers" i.e what GNC demands to be sold in a given period and high average sale, very little commission will be made as mostly 3rd party products carry commission, GNC wants you to peddle their products first and foremost. The customers goals are not central to GNC's mission, just maximizing profits at the expense of gullible customers and heartless employees.