DOSBox  was still in its infancy then, and the DOS emulation in Windows was...less than one hundred percent compatible with all the hardware tricks various DOS games used to squeeze the last ounce of performance out of the hardware. (In the DOS days, it was common practice for application programs, especially games, to directly deal with I/O ports, interrupts, DMA, etc.)
 A DOS boot disk is similar to a bootable Linux CD / DVD -- removable media containing an OS. In this case, you mainly use it to customize the loaded drivers on a per-game basis. Regardless of how much physical memory you have, in DOS only 640K is conveniently addressable , so it's very important to selectively load only the drivers a specific game needs.