Pros
You learn a lot about technology and become trained in hardware repair. Working full time you get healthcare benefits, which is great, and there are 401k matching options. The stress from this job will encourage you to seek a better job with better compensation. The skills you learn here are valuable and you can build on them elsewhere.
Cons
Always understaffed and encouraged to take on next-to-impossible repairs to make people happy, but they won't be because they want something that teeters on the edge of reality. The appointment system makes clients unhappy and they are not long enough to accurately solve issues. If helping people was the actual priority, they would be longer. If creating a positive work environment was a priority, there would be more gaps in the appointments to allow people to get a break since consistent appointments often result in no breaks. The push to sell unnecessary items and memberships leaves many people unhappy, which is partially the company's fault for not properly advertising what exactly the Geek Squad does. It's hard to feel comfortable selling an expensive membership to the elderly because they don't know how to use a computer. It could take five minutes every day to just answer simple questions, but the metrics of selling services are more important than being a nice person.