Dear ShaoBao,
I am Arun from India. I have around 7 years of experience into internet marketing. I am a Google adwords certified professional also.
I have worked on several accounts across different countries and different businesses.
Having appropriate negative keywords would help you to stop wasting the money on irrelevant traffic also gives us scope to drive quality traffic to the website, which inturn help you to improve the performance (leads, purchase, download etc.,)
Please let me know what is your website. If you are advertising in adwords already, would you be able to send me a report (search query report), so i can analyze the same and give you appropriate negative keywords and few keyword suggestions too.
Please let me know your comments.
Thanks,
Arun