This is an interesting OSPFv3 command. There are some things you can and can’t do with it. It behaves the same as IPv4 OSPF (from what I can see).
Say you want to advertise just a single address from a range within a set of subnets, but you don’t want the rest of the subnets appearing in neighbor tables, you can do:
summary-address 1be1::/16 not-advertise
Alternatively, you can’t do the following:
summary-address 1be1:5::/32 not-advertise
This is because neighbor routing tables will simply see the 1be1::/16 route, therefore making the 1be1:5::/32 network still reachable. This is confirmed by pinging devices in the 1be1:5::/32 network.
Note: On some other vendors the command is Summary-address.