Adding Clustered Storage, Why do i need to create a windows volume first?

I have 2 drives that are  located on an iSCSI target. I am adding one as a quorum drive and the other as Clustered storage.

I have gone through creating the iSCSI target, initiator and linking the two. I can see the disks in Disk Manager and brought them online.
In this state, i can add them as cluster storage, but they wont work as a quorum drive. To make one work as a quorum drive, i need to create a volume in Disk Manager on the disk.

My questions are:

1. Why can i add the disks in cluster manager without a volume created?

2. Why do i need to add a volume before i can use the drive as a quorum drive?

3. Do i need to add a volume via Disk manager for any storage Im using in the cluster, such as for sql server files?

Thanks!