Pros
You get to interact directly with clients and know them on a personal level. You will end up becoming a jack of all trades (expert in none). Also you will learn how not lie but rather omit key facts while keeping a straight face.
Cons
You will get told that the new WMS system is the gold standard but you later find out that it is fools-gold. The company has 2-3 experts in the entire company and they say how they will train you but everyone is still waiting. Client turn around is extremely high and most end up leaving to completion so you end up and continuous start up mode. It is understood that a 3PL changes quickly but priorities change hour by hour making it impossible to plan. Staff is over worked to the point that they just do not even care anymore. If you come to an interview just ask the manager if you can speak to some currently employees to get feedback. There faces will say it all.