These interrupts are used for various tasks like detecting the system memory layout, configuring VGA output and modes, and accessing the disk early in the boot process.
It is not necessary to use all of the possible entries: it is sufficient to populate the table up to the highest interrupt vector used, and set the IDT length portion of the IDTR accordingly.
The IBM PC (BIOS and MS-DOS runtime) does not follow the official Intel layout beyond the first five exception vectors implemented in the original 8086.
Interrupt 5 is already used for handling the Print Screen key, IRQ 0-7 is mapped to INT_NUM 0x08-0x0F, and BIOS is using most of the vectors in the 0x10-0x1F range as part of its API.
This has never been officially supported by Microsoft, but was not programmatically prevented on its operating systems until 64-bit versions of Windows, where a driver that attempts to use a kernel mode hook will cause the machine to bug check.