Pros
The number one reason for me is the opportunity to work with a diverse group of people. As you work with your colleague you'll get to know more about them and in turns get to embrace their backgroup. Also, depends on the job role you might get the opporutunity to work in many cross-functional projects, which allows you learn about what others are doing and it might even give you an opportunity to trasfer down the road and learn new skills set. The company is also big on gender inequality and they have a pretty good (3 months) maternity leave policy.
Cons
While HSBC is a strong international bank, its reputation in North America is pretty weak, especially on the West Coast . A lot of people still remember that HSBC was once the troubled Household bank and they want no part of it. Career advancement is pretty standard but it probably will help if you know your senior management pretty well. Once you become a manager though it's pretty hard to move up unless you are willing to pull extra 15-20 hours a week. Sometimes the perception is that those who worked (or forced to work) are the ones deem to be the better workers (which is not always true!)