I use surfactant and dawn dish soap, 5-6 oz per 100, considering the cost of herbicides. I also think the soap helps when I'm rinsing the tank and lines afterwards.
I've used just soap when my local guy was out of surfactants and it seemed to do ok but added extra.
I use both but prefer surfactant. I'm appears to me to be better doesn't foam up in the tank as bad and is cheap enough. If I'm out dawn is better than nothing.