I guess it depends on how the brewery is organized, but I am mostly referring to small breweries. Since the fermentation takes several days (and will keep equipment busy for several days) and mashing/boiling a few hours, do they mash every day?
It depends on the breweries. But most of them have a significant number of fermenters, and they will need to do multiple brews to fill up the fermenters.
For instance, one of the new breweries in my area has to do two brews to fill up a fermenter and they normally do this on subsequent days. Since they're small.
However, a larger brewery near me, literally has a round the clock brewing cycle, so they have two shifts (or more) of brewers, but still a craft brewery. They have a LOT of fermenters, and they can barely cope with demand, mainly because it's a lagered ale as their primary beer (a Kolsch, but not made in Koln) so they have longer fermentations and a cold room for conditioning.
Other smaller breweries will only brew if they have space and demand, any risk of the beer not being sold will reduce the amount of brews they do.
There's other places which have enough downtime in their brewing schedule that they do Contract Brewing, so someone will pay them to brew on their behalf (and they say they're a brewery, which I have problems with ;)) and the results of that beer will be made and fermented and the contracted brewery and there'll be a time frame where the beer has to be removed from the brewery.
For sure it depends on the size of the brewery. At our brewery in Houston we do mash every day because we're pushing our products hard in the market.