Use of bigger fermentors?

I have been looking at microbrewery rigs and how they differ from the smaller home brew setup. I have noticed lots of breweries have fermenters and/or brite tanks that are normally double the size of the boil kettle. For example a 3bbl brewery will have 3 6bbl fermenters. Is it because they are planning ahead if they want to expand? Or do they do a double brew day of some sort? If someone can please explain this to me I would appreciate it. Thank you!

Multiple brews to fill a ferm is pretty common. Commercially I have done multiples into a ferm in 2, 3 and even 12 knockouts/tank.

So would you add your yeast after you filled the tank up full or after the first day?

Or do you brew all the batches on the same day?

Add yeast on 1st knockout, brews done as close to back to back as possible.