IPv4 is not the only layer-3 protocol. We have IPv6, and Cisco has supported others, too.
You could, for example, have something like this:
no ip address
ipv6 address 2001:db8:1234:5678:90ab:cdef:1111:2222/64
The VLAN interface in this example is still active at layer-3 (IPv6 is a layer-3 protocol, too) even without an IPv4 address. With no layer-3 addressing, it is still an active layer-2 interface, and you can do other things like apply layer-2 ACLs. It is much like a physical interface, except that it applies to the entire VLAN on that switch.
shutdown command actually stops all processing on the interface, regardless of any other configuration on the interface.