We have a small roof with 1/3 of our panels facing east, 1/3 facing west, and 1/3 facing south. Given a sufficiently large roof, it would theoretically make sense to have all of the panels facing south.
However, due to the fact that PG&E keeps shifting our peak hours, we actually get more credit for producing in the afternoon, so when we expand our house, I'm planning on having all the panels (as much as possible) on the west-facing roof.
Also, we plan to install air conditioning at that time, so it will be helpful to be able to handle that peak demand.
> theoretically make sense to have all of the panels facing south
It depends what you are optimising for. East/west makes a lot of sense to optimise for morning and evening sun. Especially as during the middle of the day electricity prices usually drop due to excess solar.