Should I apply for the scholarships if I currently have a RA position in my supervisor lab? I am a M.Sc. graduated and I will start my PhD in September and in a top university abroad (Canada). My supervisor guaranteed a yearly stipend during my studies as long as I am in good academic standing from his own grants.
Recently, department secretary advertised the PhD scholarship competition of the university which covers the stipends of students during their PhD studies. The amount of scholarship is just slightly better than my current RA funding (~2k per year difference), so it is not a major monetary benefit in that. More over, I wondering if accepting the scholarship leads the professor to pay less attention to my project as he is not under some pressure to complete the projects that he did not receive grants for. On the other hand, accepting the scholarship may give the students some degree of security about their funding (e.g. if they find conflicts with their advisor in future and want to change advisor). 
All in all, I would like to know if is it a good idea to accept an scholarship instead of the RA funding of the lab you work in?
You should get scholarship if:


You want more money
You want to make your supervisor happy
Self-esteem (because you can self-fund yourself)
Something to put on your resume
Easier if you want to change supervisor
The scholarship is guaranteed (if offered) whereas your lab's yearly stipend is not. Your supervisor only gives you verbal agreement, but she might change her mind. Do you have a contract with her to guarantee your payment for the next 4 years?


Generally, PhD student is expected to secure a scholarship. Your supervisor is responsible to guide you for your PhD with or without your scholarship.

You may ask your supervisor to give you top-up.

You should not get scholarship if:


Your supervisor wants to employ you and pay you salary
You want to work while doing your PhD


Otherwise, why not?