Pros
Best reason is gaining the experience. When I first started working at d-mars I was an okay designer, after working with other designers I learned so much from everyone. Each designer was good in something, one designer was good in photoshop, other in illustrator and the other in dreamweaver, I was always good in indesign. We all learn from each other and share graphic goodies such as vectors, juicedrops, images etc. I not only gain experience in design, but also in communicating with clients that is very important. I would always be nervous to call clients and write down what i was going to say. Now I don't have to. Once you gain more experience you are valued alot more and have more knowledge to be your own boss. That is one thing I am aiming for to gain the experience and to make my own firm some day.
Kontras
The Pressure!!!! If a project is due you have to work hard and over time and that is alot of pressure. Being a designer can give you alot of stress. My boss would always pressure me to finish this project, while I have 3 other projects to finish. I would sometime have clients making 20 changes, things that is not even your fault, stuff like can you add this text and image can you delete this text or image like 20 times. Then the deadlines you have to meet for all these projects.