For internal services, you probably want to have them fail over between sites. Dynamic routing protocols will let you do that.
If you use a loopback interface for your service, you can share the IP address between two different servers, even on the same LAN.
A nifty hack that’s possible in IP networks is the ability to share an IP between servers thousands of miles apart.
Anycasting is a way to scale geographically by having multiple servers sharing the same IP address.