There are many factors that can be discussed on this issue,

two things that pop up on my mind are that many storage domains will make your Data Center be more robust and flexible, since you can maintain part of the storage domains which could help with upgrading your storage server in the future or fixing issues that might occur in your storage, without moving your Data Center to a non operational state.

One storage domain is preferrable if you want to use large disks with your VMs that small storage domains does not have the capacity to do so