Okay -- I need to be more specific. Our main USTA adult leagues in NorCal are April start with 3 doubles and 2 singles for each match.
Our teams have been extremely successful for a small (6 court) club. We all spend a lot of time practicing -- and that includes a lot of different partnerships -- in social and competitive situations. Some players even make time for some tournaments -- good mental conditioning.
Also -- a plain fact of partnerships is practice restraints. The best partners are those who are able to find the time to practice together, and who are on the same page as far as dedication.