Jacob,
When you create an SVI interface because is a virtual interface without any physical associations, at least you must have one L2 VLAN created for it with a connected device or host on a switchport to associate it with that newly created SVI interface in order for the SVI interface to be fully up and functional. A virtual SVI interface without any L2 vlan association in a switchport will just be an idle SVI interface, this would be the case when no L2 VLAN is associated with L3 interface the expected output of " show ip interface brief " for the SVI will be Up/Down.
What is the difference in creating L3 Vlan with L2 and with out L2 ?
Same as above answer, once you create L2 VLAN in vlan database and connect a device or host on a switchport that will bellong to L3 SVI network that you have created, the SVI interface will be a fully functional as well as fully routable and be able to route between any other L3 interfaces or SVI you have similarly created.
HTH
-Jorge
Jorge Rodriguez