You may want to review just how Linux boots from BIOS. It's a multi-step process, and the first few steps all require that the BIOS speak to the drive in the binary language of moisture vaporators (which are very similar to binary load lifters in most respects.)
Specifically, the boot process starts with BIOS looking for the MBR, then loading and executing whatever code it finds there. This code then reads the next part of the boot loader, and executes that, and then that loads your kernel and transfers control to it.
Because the BIOS code for reading from the disk is so old, it deals only with 512 byte blocks and uses a 32 bit unsigned integer to store block numbers. That means that any operations involving the boot loader can only see up to 232 * 512 bytes into the drive, or 2.2 terabytes. If you are still booting from BIOS then your /boot partition needs to exist entirely below the 2TiB barrier, or the boot loader will not be able to load from it. The start and end of the partition need to both have block numbers less than 232 or the filesystem will not be readable by the boot loader.
The same limit applies to old fashioned MBR partition tables. This is why your disk is formatted in the newer GPT style, which uses 64 bit numbers giving it a limit of 9400000000 TB. While you may be able to buy a drive bigger than that on Amazon, you may find that it isn't quite as reliable as you would hope.
Modern systems no longer use BIOS for booting but use UEFI instead. UEFI also uses 64 bit numbers to address disk blocks, so it is not affected by the 2.2 terabyte limit, only the 9.4 zettabyte limit that GPT disks have.
So, to answer your question, here are the risks associated with using oversized disks on a legacy BIOS system:
If the disk is used for booting and the /boot partition is not located entirely within the first 2.2 TB, it will not boot.
That's it. Once your BIOS reads the /boot partition it transfers control to the Linux kernel, which has no limitations on what blocks it can read. Every other filesystem can be as large as it likes, and wherever it wants to be.
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