It probably would not make much of a difference to do it once a week. But usually I take a shot- three days off- shot approach with deca. It theoretically is better for overall blood volumes... but the difference is minimal.
I always did it several times, but my trainer is an IFBB pro(who won the canadian, european, and world championships), as well as being the most impressive trainer I've ever seen, kinda gave me shit for doing it more than 1x per week