We recently moved VMs from one failover cluster to another and found out that Veeam treats these as new VMs, which also means the Backup Copy treats them as new VMs. It takes us 3 weeks to run a full backup copy offsite. Obviously, that's both an annoyance and a potential job killer if something happens during that time when in reality the only that that has changed are some xml files.
I've also had to restart replication this year after v8 to v9 upgrade somehow broke the replication. Again, I should be able to re-use what's already offsite to catch up the replication rather than starting from scratch.
The replication option allows for seeding and VM mapping, but the Backup Copy does not and I think it absolutely should. If I have to restart another 3-week offsite copy again I think I'll start looking for a new Hyper-V backup copy utility.