Should graduate applicants follow instructions by department NOT to contact potential advisors? I am applying for doctoral programs in biostatistics and have read multiple places to attempt to set up contact with a potential advisor before applying.  

What if the department website specifically says to not contact potential advisors? There is a research lab I am very interested in joining (my top pick), but I still should not contact this professor, right?

Here's the exact wording of the website: 


  "Should I contact faculty about RA opportunities?
  No. All applications are reviewed by our admission committee and students do not need to (nor can they) try to find their own mentors prior to admissions. Having an interested faculty member in no way influences the admission process, which is based on an evaluation of your application only."
There are multiple practical reasons for not asking you not to contact advisors prior to admission:


Advisors may not know how many RA positions they will have available until later in the year, and departments do not want that to discourage people from applying.
They may have an established procedure for allocating students to research groups; "jumping the gun" would therefore be discouraged.
They don't want undue influence from various faculty members lobbying the admissions committee in support of "their" candidates.


Note that this is also because at many schools—particularly in Europe—individual faculty members are responsible for advertising their open positions. This is not the normal procedure in the US, thereby leading many schools to explicitly state that students should not directly petition individual faculty members.