Do I really need two separate iSCSI vlans connecting hosts to SAN?

I see its best practice to have two vlans - vlan 50 for SPA 1 and SPB 1 vlan 60 for SPA 2 and SPB 2

What are the drawbacks to using just one vlan dedicated to all iscsi traffic?

If it matters its just 5 host with 4 nics.