The 93XX accounts added together make up your operating budget. Your operating budget can be considered as one pool of money. In other words, as long as you have money in your overall operating budget, even if you "overdraw" a particular 93XX account, you will still be covered.
The different accounts, however, are there to help you keep track of where your money is going. If you find that you are "overdrawing" certain accounts and under-spending in others, it is a good idea to reallocate your funds to better reflect your actual spending. This will help you see more clearly where you stand financially at any given point throughout the year. The easiest time to reallocate funds among 93XX accounts is during Phase II of the budget prep