Not just company resources, but also customer resources. Part of this is obvious; if your fanbase only has a certain amount of money each month for gaming stuff, you don't want to be in a position where you need to take in more than that. However, there's another consideration: whale saturation.
Ideally, if you're WotC, you want your big fans buying all of your product. However, your customers only have so much money in a month. If you release too many products too quickly, then even your hardcore fanbase are going to be unable or unwilling to buy everything you release. Once people are no longer able to afford to buy each book as it comes out, it removes the urgency of "I must buy this!" So not only do they not buy the extra stuff you put out, they're not necessarily buying as much as they were before you saturated the release schedule.
Obviously, the point where that happens will differ from person to person depending on personal finances and willingness to allocate money for nerdery. But if your goal is to count on whales, you have to keep a close eye on that balance. Once someone stops auto-buying your stuff, it can be really difficult to bring them back, even if you cut back on the production line later on.
