For me it depends on the job and size of the job! But, for a new house I usually get 50% down upon acceptence of the contract, 25% after the rough inspection. The final 25% upon the final inspection. The reason I want to have a total of 75% of my money after the rough is because 80-85% of my work is done!, why should I only have 66% of my money? Also, if the homeowner decides to pull a fast one and bring in another plumber for the finish I would'nt take such a big hit or if they take a year to get ready for finish or run out of money ete,etc...
Plus the old 33%,33% and 33% was written by some old fashion lawyer and if you notice everybody loses 1% , now that is not a typical lawyer move is it?!