Seniority grants you better positions (even ranking membership and chairmanships) in committees, which gives the Rep the ability to greatly influence legislation. Example: Ted Stevens (R-AK) was chairman of the Senate Appropriations Committee from 97-05 which allowed him to direct an obscene amount of federal projects to Alaska. 

Perlmutter, if he is able to keep his seat and rise to chairman of his committee (Space, Energy, and Environment), he will be a position to greatly support NREL and the blossoming Aerospace Industry in Colorado. 

In other words, if you are going to have a congressperson from a party you don't support, you would still like them to have Seniority to influence and protect interests vital to your region.